The roots are in red. After the 12th fret, the forms repeat. Check the full neck of the G major scale then check out all the major scales forms to see how they all fit together.
Major Scale Forms
You can see how these relate to the full fretboard diagram shown above.
The roots (tonics) of the scales are in red.
Root on 6th string
Form 1
G major scale, 1st finger on the 3rd fret.
Form 2
G major scale, 1st finger on the 2nd fret.
Form 3
This scale form has 2 variations. In the first, you stay in the same position. In the second variation, you shift up 2 frets.
Form 3
G major scale, 1st finger on the 12nd fret. Or substitute the first finger for the open string and play this in open position.
Root on 5th string
Form 1
Form 2
Form 3
Form 3, 2nd variation
G major scale, 1st finger on the 12nd fret. Or substitute the first finger for the open string and play this in open position.