piano chord
C♯9
C♯1E♯3G♯5B♭7D♯9
A dominant seventh carrying a ninth on top.
Written the other way round it is D♭9 — the same twelve keys on a piano, a different piece of notation.
What is true of it
C♯9 is C♯, E♯, G♯, B and D♯ — 1, 3, 5, b7 and 9 counted from C♯.
On an instrument that cannot reach all 5, the 5 and 1 go first, in that order.