Scales to Play Over A6
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 A6 chord contains the notes A – C# – E – F#. Any scale that includes every one of those 4 tones fits over it — from the root A, that means A Major, A Major Pentatonic, A Rock 'n' Roll, A Lydian, A Mixolydian, A Dorian Bebop, A Mixolydian Bebop, A Half Whole Diminished and A Gypsy Major. Start with the first scale listed: it is the most common choice, and the others color the same chord tones differently.
A6 is also diatonic to 3 major keys: A major (relative minor F#m), D major (relative minor Bm), E major (relative minor C#m). 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.