Scales to Play Over F#7
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 F#7 chord contains the notes F# – A# – C# – E. Any scale that includes every one of those 4 tones fits over it — from the root F#, that means F# Mixolydian, F# Dorian Bebop, F# Mixolydian Bebop, F# Half Whole Diminished, F# Spanish and F# Gypsy Major. Start with the first scale listed: it is the most common choice, and the others color the same chord tones differently.
F#7 is also diatonic to one major key: B major (relative minor G#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.