Scales to Play Over F#m(add9)
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#m(add9) chord contains the notes F# – G# – A – C#. Any scale that includes every one of those 4 tones fits over it — from the root F#, that means F# Natural Minor, F# Melodic Minor, F# Harmonic Minor, F# Rock 'n' Roll, F# Dorian, F# Dorian Bebop and F# Gypsy Minor. Start with the first scale listed: it is the most common choice, and the others color the same chord tones differently.
F#m(add9) is also diatonic to 2 major keys: A major (relative minor F#m), 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.