The 4th pattern G Major scale takes it’s root note positions from the E shape open chord. When looking at the open E chord, the root notes are located on the open Top and Bottom E strings and the 2nd fret D string.
E
Important: The notes used in the G Major scale are G, A, B, C, D, E, F#, there is one sharp in the G Major scale.
If we take a look at the scale on the fretboard, you will see something like the following pattern… the root notes are marked with the “X“
|| | $1.2.$3.2.$4.2.$5.2.$6.2 | $1.X.$2.3.$5.3.$6.X | $3.4.$4.4 | $1.5.$2.5.$3.5.$4.X.$5.5.$6.5 |
Note: In the diagram above it’s the fret numbers that are indicated not the scale degrees, and it isn’t the way you would normally write out a scale using TAB, it’s just to illustrate the fingering pattern of the scale. 
When playing this scale on the guitar, I normally start on the lowest pitch root note, the 3rd fret Bottom E string with the middle finger, and play up to the highest pitch note of the scale, 1st string 5th fret, which is an A note.
| $6.3 5 $5.2 3 5 $4.2 4 5 $3.2 4 5 $2.3 5 $1.2 3 5 |
Descending back to the lowest pitch note of the scale, the F# on the 2nd fret bottom E string.
| $1.5 3 2 $2.5 3 $3.5 4 2 $4.5 4 2 $5.5 3 2 $6.5 3 2 |
Then back up in pitch to the G root note on the 3rd fret bottom E string.
| $6.2 3 |