guitar chord
A♯9
A dominant seventh carrying a ninth on top.
Written the other way round it is B♭9 — the same twelve keys on a piano, a different piece of notation.
Every fingering that fits a hand
x10111
moderate
x1011x
open · no 5
x10114
hard · no 5
x10314
hard · no 5
686768
hard · barre
What is true of it
A♯9 is A♯, C𝄪, E♯, G♯ and B♯ — 1, 3, 5, b7 and 9 counted from A♯.
C𝄪 is a double sharp, and it has to be: every letter from A♯ upwards is used once, so the 3 cannot be written any other way.
On an instrument that cannot reach all 5, the 5 and 1 go first, in that order.
The easiest of the 5 fingerings below is x10111: 4 fingers, held at the 1st fret.
1 of them use open strings, which is what makes a shape quiet to change to.
1 of the 5 need a barre.
1 string stays silent.
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♯9/C𝄪
xx0111
A♯9/E♯
11011x
A♯9/G♯
43033x
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.