Plotting XRD pattern in Gnuplot

Question

I wish to plot a XRD pattern using Gnuplot. The data file is given below

# User : 
# Journal : 
# Sample Details : 
# Col 1: 2theta (deg.), Col 2: Intensity (a.u.)  
20  88
20.05   92
20.1    96
20.15   88
20.2    84
20.25   100
20.3    94
20.35   84
20.4    78
20.45   81
20.5    86
20.55   92
20.6    85
20.65   74
20.7    83
20.75   74
20.8    87
20.85   67
20.9    85
20.95   83
21  90
21.05   81
21.1    87
21.15   84
21.2    83
21.25   84
21.3    86
21.35   92
21.4    92
21.45   73
21.5    97
21.55   96
21.6    88
21.65   95
21.7    93
21.75   83
21.8    91
21.85   91
21.9    76
21.95   85
22  89
22.05   87
22.1    72
22.15   85
22.2    71
22.25   68
22.3    75
22.35   63
22.4    64
22.45   76
22.5    72
22.55   78
22.6    62
22.65   80
22.7    80
22.75   78
22.8    85
22.85   62
22.9    74
22.95   84
23  73
23.05   76
23.1    83
23.15   48
23.2    74
23.25   79
23.3    75
23.35   70
23.4    94
23.45   80
23.5    79
23.55   69
23.6    73
23.65   55
23.7    72
23.75   59
23.8    87
23.85   76
23.9    70
23.95   76
24  74
24.05   76
24.1    89
24.15   79
24.2    84
24.25   72
24.3    69
24.35   74
24.4    72
24.45   85
24.5    65
24.55   85
24.6    68
24.65   71
24.7    70
24.75   70
24.8    75
24.85   73
24.9    79
24.95   76
25  78
25.05   68
25.1    67
25.15   62
25.2    72
25.25   65
25.3    78
25.35   74
25.4    67
25.45   77
25.5    70
25.55   82
25.6    80
25.65   64
25.7    71
25.75   67
25.8    70
25.85   73
25.9    80
25.95   69
26  61
26.05   82
26.1    86
26.15   83
26.2    88
26.25   68
26.3    78
26.35   66
26.4    71
26.45   69
26.5    61
26.55   73
26.6    74
26.65   83
26.7    72
26.75   82
26.8    84
26.85   72
26.9    68
26.95   72
27  63
27.05   66
27.1    68
27.15   65
27.2    75
27.25   72
27.3    66
27.35   58
27.4    67
27.45   73
27.5    74
27.55   84
27.6    80
27.65   82
27.7    70
27.75   71
27.8    70
27.85   76
27.9    73
27.95   85
28  82
28.05   75
28.1    70
28.15   85
28.2    80
28.25   96
28.3    126
28.35   173
28.4    219
28.45   270
28.5    214
28.55   158
28.6    105
28.65   78
28.7    75
28.75   82
28.8    83
28.85   74
28.9    79
28.95   77
29  61
29.05   75
29.1    75
29.15   65
29.2    69
29.25   79
29.3    68
29.35   78
29.4    74
29.45   57
29.5    75
29.55   65
29.6    69
29.65   83
29.7    72
29.75   69
29.8    65
29.85   68
29.9    89
29.95   79
30  84
30.05   110
30.1    129
30.15   146
30.2    150
30.25   136
30.3    117
30.35   81
30.4    72
30.45   85
30.5    75
30.55   71
30.6    70
30.65   72
30.7    87
30.75   67
30.8    71
30.85   75
30.9    80
30.95   76
31  78
31.05   72
31.1    66
31.15   85
31.2    61
31.25   62
31.3    69
31.35   75
31.4    51
31.45   48
31.5    55
31.55   77
31.6    66
31.65   84
31.7    64
31.75   69
31.8    74
31.85   53
31.9    77
31.95   68
32  74
32.05   53
32.1    67
32.15   61
32.2    68
32.25   77
32.3    62
32.35   57
32.4    62
32.45   62
32.5    62
32.55   66
32.6    56
32.65   55
32.7    62
32.75   61
32.8    67
32.85   74
32.9    49
32.95   66
33  82
33.05   57
33.1    59
33.15   61
33.2    62
33.25   74
33.3    60
33.35   72
33.4    66
33.45   71
33.5    58
33.55   66
33.6    59
33.65   66
33.7    53
33.75   70
33.8    52
33.85   66
33.9    58
33.95   65
34  47
34.05   51
34.1    56
34.15   55
34.2    77
34.25   70
34.3    64
34.35   59
34.4    62
34.45   51
34.5    62
34.55   48
34.6    45
34.65   59
34.7    65
34.75   64
34.8    83
34.85   75
34.9    125
34.95   149
35  152
35.05   120
35.1    84
35.15   76
35.2    70
35.25   63
35.3    68
35.35   51
35.4    64
35.45   62
35.5    58
35.55   63
35.6    67
35.65   68
35.7    62
35.75   58
35.8    59
35.85   48
35.9    53
35.95   55
36  54
36.05   56
36.1    49
36.15   53
36.2    66
36.25   60
36.3    63
36.35   61
36.4    48
36.45   67
36.5    61
36.55   50
36.6    48
36.65   46
36.7    70
36.75   54
36.8    62
36.85   62
36.9    45
36.95   56
37  44
37.05   59
37.1    58
37.15   53
37.2    49
37.25   49
37.3    54
37.35   51
37.4    48
37.45   49
37.5    56
37.55   47
37.6    53
37.65   50
37.7    47
37.75   48
37.8    64
37.85   61
37.9    56
37.95   44
38  44
38.05   43
38.1    45
38.15   51
38.2    61
38.25   48
38.3    39
38.35   58
38.4    50
38.45   56
38.5    49
38.55   54
38.6    47
38.65   47
38.7    46
38.75   49
38.8    43
38.85   50
38.9    51
38.95   60
39  69
39.05   46
39.1    68
39.15   44
39.2    42
39.25   46
39.3    52
39.35   43
39.4    46
39.45   52
39.5    57
39.55   46
39.6    48
39.65   47
39.7    51
39.75   61
39.8    48
39.85   53
39.9    59
39.95   46
40  53
40.05   51
40.1    49
40.15   56
40.2    49
40.25   50
40.3    52
40.35   58
40.4    62
40.45   99
40.5    119
40.55   161
40.6    135
40.65   163
40.7    130
40.75   105
40.8    80
40.85   68
40.9    53
40.95   55
41  53
41.05   54
41.1    59
41.15   56
41.2    53
41.25   52
41.3    46
41.35   47
41.4    44
41.45   57
41.5    49
41.55   48
41.6    42
41.65   45
41.7    46
41.75   48
41.8    44
41.85   51
41.9    45
41.95   54
42  44
42.05   46
42.1    43
42.15   53
42.2    50
42.25   38
42.3    42
42.35   51
42.4    51
42.45   42
42.5    36
42.55   36
42.6    53
42.65   44
42.7    38
42.75   45
42.8    55
42.85   33
42.9    50
42.95   58
43  48
43.05   46
43.1    51
43.15   44
43.2    58
43.25   47
43.3    47
43.35   59
43.4    42
43.45   50
43.5    50
43.55   45
43.6    48
43.65   51
43.7    38
43.75   51
43.8    57
43.85   49
43.9    59
43.95   40
44  41
44.05   39
44.1    37
44.15   43
44.2    43
44.25   52
44.3    50
44.35   46
44.4    41
44.45   48
44.5    44
44.55   40
44.6    47
44.65   39
44.7    49
44.75   49
44.8    44
44.85   38
44.9    44
44.95   53
45  46
45.05   51
45.1    31
45.15   38
45.2    51
45.25   42
45.3    47
45.35   46
45.4    37
45.45   66
45.5    53
45.55   40
45.6    45
45.65   39
45.7    47
45.75   39
45.8    45
45.85   38
45.9    48
45.95   42
46  35
46.05   46
46.1    45
46.15   34
46.2    55
46.25   39
46.3    35
46.35   50
46.4    32
46.45   49
46.5    50
46.55   36
46.6    46
46.65   51
46.7    41
46.75   41
46.8    53
46.85   54
46.9    50
46.95   43
47  44
47.05   61
47.1    36
47.15   43
47.2    48
47.25   38
47.3    46
47.35   48
47.4    51
47.45   42
47.5    51
47.55   37
47.6    40
47.65   49
47.7    33
47.75   36
47.8    41
47.85   49
47.9    39
47.95   42
48  58
48.05   51
48.1    43
48.15   48
48.2    46
48.25   34
48.3    44
48.35   39
48.4    44
48.45   46
48.5    35
48.55   35
48.6    51
48.65   43
48.7    45
48.75   54
48.8    48
48.85   41
48.9    49
48.95   52
49  36
49.05   42
49.1    38
49.15   44
49.2    44
49.25   38
49.3    49
49.35   54
49.4    52
49.45   39
49.5    41
49.55   66
49.6    51
49.65   38
49.7    34
49.75   52
49.8    46
49.85   60
49.9    47
49.95   45
50  68
50.05   66
50.1    68
50.15   89
50.2    133
50.25   137
50.3    125
50.35   124
50.4    103
50.45   88
50.5    72
50.55   59
50.6    56
50.65   46
50.7    39
50.75   51
50.8    27
50.85   45
50.9    41
50.95   43
51  51
51.05   49
51.1    45
51.15   38
51.2    48
51.25   43
51.3    42
51.35   44
51.4    45
51.45   49
51.5    40
51.55   43
51.6    37
51.65   50
51.7    47
51.75   37
51.8    39
51.85   43
51.9    42
51.95   40
52  45
52.05   34
52.1    32
52.15   43
52.2    37
52.25   47
52.3    62
52.35   36
52.4    45
52.45   36
52.5    37
52.55   38
52.6    37
52.65   35
52.7    38
52.75   47
52.8    40
52.85   50
52.9    50
52.95   44
53  44
53.05   35
53.1    46
53.15   43
53.2    40
53.25   57
53.3    29
53.35   39
53.4    39
53.45   43
53.5    51
53.55   44
53.6    53
53.65   40
53.7    41
53.75   59
53.8    46
53.85   46
53.9    57
53.95   52
54  48
54.05   50
54.1    40
54.15   42
54.2    46
54.25   48
54.3    47
54.35   42
54.4    49
54.45   43
54.5    43
54.55   54
54.6    44
54.65   40
54.7    45
54.75   34
54.8    42
54.85   40
54.9    34
54.95   43
55  51
55.05   56
55.1    42
55.15   37
55.2    41
55.25   49
55.3    53
55.35   46
55.4    47
55.45   39
55.5    43
55.55   43
55.6    41
55.65   38
55.7    36
55.75   55
55.8    45
55.85   37
55.9    47
55.95   50
56  46
56.05   51
56.1    51
56.15   56
56.2    31
56.25   44
56.3    41
56.35   45
56.4    45
56.45   49
56.5    45
56.55   60
56.6    30
56.65   38
56.7    51
56.75   54
56.8    45
56.85   38
56.9    40
56.95   41
57  36
57.05   35
57.1    45
57.15   41
57.2    49
57.25   36
57.3    38
57.35   43
57.4    43
57.45   41
57.5    42
57.55   42
57.6    41
57.65   39
57.7    37
57.75   48
57.8    42
57.85   56
57.9    45
57.95   39
58  51
58.05   40
58.1    47
58.15   39
58.2    46
58.25   37
58.3    41
58.35   36
58.4    50
58.45   42
58.5    58
58.55   36
58.6    59
58.65   57
58.7    57
58.75   68
58.8    61
58.85   68
58.9    58
58.95   54
59  53
59.05   59
59.1    48
59.15   49
59.2    42
59.25   49
59.3    45
59.35   38
59.4    44
59.45   54
59.5    37
59.55   52
59.6    62
59.65   70
59.7    73
59.75   88
59.8    69
59.85   62
59.9    60
59.95   51
60  59
60.05   51
60.1    45
60.15   45
60.2    39
60.25   55
60.3    48
60.35   45
60.4    34
60.45   47
60.5    32
60.55   40
60.6    40
60.65   54
60.7    35
60.75   50
60.8    40
60.85   34
60.9    39
60.95   31
61  27
61.05   45
61.1    47
61.15   41
61.2    34
61.25   46
61.3    42
61.35   33
61.4    45
61.45   41
61.5    31
61.55   42
61.6    40
61.65   32
61.7    35
61.75   33
61.8    45
61.85   48
61.9    50
61.95   44
62  36
62.05   34
62.1    44
62.15   47
62.2    40
62.25   42
62.3    50
62.35   51
62.4    43
62.45   46
62.5    59
62.55   50
62.6    56
62.65   63
62.7    67
62.75   54
62.8    61
62.85   54
62.9    43
62.95   44
63  36
63.05   49
63.1    41
63.15   46
63.2    44
63.25   36
63.3    34
63.35   36
63.4    58
63.45   42
63.5    40
63.55   48
63.6    43
63.65   35
63.7    36
63.75   42
63.8    41
63.85   40
63.9    39
63.95   40
64  32
64.05   46
64.1    44
64.15   41
64.2    44
64.25   35
64.3    45
64.35   46
64.4    37
64.45   43
64.5    36
64.55   40
64.6    36
64.65   45
64.7    38
64.75   42
64.8    37
64.85   39
64.9    50
64.95   40
65  28
65.05   34
65.1    41
65.15   42
65.2    40
65.25   45
65.3    34
65.35   44
65.4    49
65.45   49
65.5    46
65.55   36
65.6    40
65.65   51
65.7    30
65.75   48
65.8    34
65.85   52
65.9    32
65.95   43
66  41
66.05   42
66.1    61
66.15   57
66.2    55
66.25   44
66.3    63
66.35   78
66.4    80
66.45   77
66.5    98
66.55   86
66.6    81
66.65   61
66.7    62
66.75   59
66.8    54
66.85   50
66.9    52
66.95   32
67  35
67.05   39
67.1    47
67.15   39
67.2    51
67.25   53
67.3    35
67.35   41
67.4    38
67.45   25
67.5    48
67.55   41
67.6    37
67.65   45
67.7    37
67.75   29
67.8    32
67.85   28
67.9    31
67.95   41
68  33
68.05   44
68.1    48
68.15   39
68.2    46
68.25   49
68.3    39
68.35   40
68.4    50
68.45   40
68.5    54
68.55   44
68.6    35
68.65   31
68.7    46
68.75   28
68.8    38
68.85   29
68.9    34
68.95   43
69  49
69.05   37
69.1    43
69.15   44
69.2    31
69.25   33
69.3    43
69.35   47
69.4    42
69.45   39
69.5    37
69.55   35
69.6    42
69.65   44
69.7    37
69.75   53
69.8    24

Answer 1

If I understand well, you want something like this:

To achieve this, extend your code with:

set key horizontal
plot [10:90] 'XRD_E1.dat' u 1:2 w l ls 1 notitle, 1/0 w p pt 7 ps 1.75 lc rgb "red" t 'LiCl', 1/0 w p pt 7 ps 1.75 lc rgb "blue" t 'KCl'