Scales to Play Over G6
Every chord is a subset of several scales: any scale that contains all of a chord's tones fits over it. Pick a chord to see the matching scales from its own root, the major keys the chord belongs to, and full fretboard diagrams for every scale on guitar.
A G6 chord contains the notes G – B – D – E. Any scale that includes every one of those 4 tones fits over it — from the root G, that means G Major, G Major Pentatonic, G Rock 'n' Roll, G Lydian, G Mixolydian, G Dorian Bebop, G Mixolydian Bebop, G Half Whole Diminished and G Gypsy Major. Start with the first scale listed: it is the most common choice, and the others color the same chord tones differently.
G6 is also diatonic to 3 major keys: C major (relative minor Am), D major (relative minor Bm), G major (relative minor Em). In a song from one of those keys you can also solo with the key's own major scale or its relative minor pentatonic across the whole progression, not just this chord.