Every fingering that fits a hand
545000
easy
542000
easy
547000
easy
545400
moderate
545600
moderate
What is true of it
A9 is A, C♯, E, G and B — 1, 3, 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 5 fingerings below is 545000: 3 fingers, held at the 4th 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 A, the root. Everything else is a chord tone with its degree printed in it.
With a different note underneath
A9/C♯
x45000
A9/E
045000
A9/G
342000
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.