Scales to Play Over Fdim
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 Fdim chord contains the notes F – G# – B. Any scale that includes every one of those 3 tones fits over it — from the root F, that means F Blues, F Locrian, F Half Whole Diminished, F Whole Half Diminished, F Gypsy Major 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.
Fdim is also diatonic to one major key: F# major (relative minor D#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.