What is true of it
B♭dim7 is B♭, D♭, F♭ and A♭♭ — 1, b3, b5 and bb7 counted from B♭.
A♭♭ is a double flat, and it has to be: every letter from B♭ upwards is used once, so the bb7 cannot be written any other way.
The easiest of the 1 fingering below is 3434: 3 fingers, one of them barring the 3rd fret, held at the 3rd 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.
Where its notes are on the neck
The brass dots are B♭, the root. Everything else is a chord tone with its degree printed in it.
With a different note underneath
B♭dim7/D♭
6767
B♭dim7/F♭
9a9a
B♭dim7/A♭♭
0101
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.