What is true of it
Am9 is A, C, E, G and B — 1, b3, 5, b7 and 9 counted from A.
On an instrument that cannot reach all 5, the 5 and 1 go first, in that order.
The easiest of the 1 fingering below is 2032: 3 fingers, held at the 2nd fret.
All of them use open strings, which is what makes a shape quiet to change to.
It leaves out the 5. 4 strings cannot carry 5 notes, and the 5 is the one this chord can lose without changing what it is.
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
Am9/C
x032
Am9/E
9b8a
Am9/G
0002
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.