Root on A string
x56x67
Ddim7 is the D diminished 7 chord. Its notes are D, F, A♭ and C♭. Stacked minor thirds. Its symmetrical sound makes it useful as a passing chord.
x56x67
Numbers show frets from the low E string to the high e string; x means don't play that string.
Every D, F, A♭ and C♭ on the first 12 frets. The filled dots are the root, D. Build your own shape from any nearby group.
Other D chords
Other diminished 7 chords