guitar chord
A♭dim7
Three minor thirds stacked. The seventh is doubly diminished, which is why it is written with a double flat.
Written the other way round it is G♯dim7 — the same twelve keys on a piano, a different piece of notation.
Every fingering that fits a hand
420101
moderate
420401
moderate
45340x
hard
45046x
hard
456464
hard · barre
What is true of it
A♭dim7 is A♭, C♭, E♭♭ and G♭♭ — 1, b3, b5 and bb7 counted from A♭.
E♭♭ and G♭♭ are double flats, and they have to be: every letter from A♭ upwards is used once, so the b5 cannot be written any other way.
The easiest of the 5 fingerings below is 420101: 4 fingers, held at the 1st fret.
None of them uses an open string, so this chord moves up the neck unchanged — the same shape 1 fret higher is the chord a semitone above.
1 of the 5 need a barre.
Where its notes are on the neck
The brass dots are A♭, the root. Everything else is a chord tone with its degree printed in it.
With a different note underneath
A♭dim7/C♭
x20101
A♭dim7/E♭♭
xx0101
A♭dim7/G♭♭
120101
An inversion is the same chord with a different note lowest. The name changes to a slash name because the bass is what a listener hears as the foundation.