piano chord
C♯add9
C♯1E♯3G♯5D♯9
A major triad with a ninth added and no seventh — which is what tells it apart from a ninth chord.
Written the other way round it is D♭add9 — the same twelve keys on a piano, a different piece of notation.
What is true of it
C♯add9 is C♯, E♯, G♯ and D♯ — 1, 3, 5 and 9 counted from C♯.
On an instrument that cannot reach all 4, the 5 goes first, in that order.