The standard grips this chord is usually shown with.
Bbmadd9 is Bb, Db, F and C, a minor add nine. The shape this page opens on is written x4331x, lowest string first.

Also written Bbm(add9), Bbmin(add9) or Bb-add9. The same chord either way; which spelling you meet depends on who wrote the chart.
There are 7 common shapes for Bbmadd9 on the guitar, and 22 derived voicings in 2 families.
In which keys. Every note of Bbmadd9 belongs to C# major (the vi), F minor (the iv), Ab major (the ii) and Bb minor (the i).
The common shapes, written lowest string first: x4331x, 64x56x, 688668, xx8668, x-x-11-10-11-8, x-13-11-10-13-x, x-13-11-x-13-13.
Drop 2. A close-position chord with the second voice from the top lowered an octave. Sits on four adjacent strings. Bbmadd9 has x3332x, xx8668, 8886xx, x-x-10-10-11-9, x-15-15-15-14-x, xx3526, 6435xx, x4856x.
Drop 3. The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped. Bbmadd9 has x3x321, 6x352x, x4x566, 8x866x, x-13-x-10-13-9, 9-x-10-10-11-x, 13-x-11-15-13-x, x-15-x-15-14-13.
The common shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.