Root on A string
x-9-10-11-10-x
F♯dim is the F♯ diminished chord. Its notes are F♯, A and C. It is the same chord as G♭dim. A compact, tense triad. Every interval in this voicing is a chord tone.
x-9-10-11-10-x
Numbers show frets from the low E string to the high e string; x means don't play that string.
F♯dim is the vii° chord in G major. That makes it a natural fit in songs written in those keys.
Every F♯, A and C on the first 12 frets. The filled dots are the root, F♯. Build your own shape from any nearby group.
Other F♯ chords
Other diminished chords