piano chord
C♯m6
C♯1E♭3G♯5A♯6
A minor triad with a major sixth added, which is why it is not simply a minor chord with a flat seventh.
Written the other way round it is D♭m6 — the same twelve keys on a piano, a different piece of notation.
What is true of it
C♯m6 is C♯, E, G♯ and A♯ — 1, b3, 5 and 6 counted from C♯.
These are also the notes of A♯m7♭5/C♯ and B♭m7♭5/C♯. Which name is right depends on what is underneath and what came before — the notes alone do not decide.
On an instrument that cannot reach all 4, the 5 goes first, in that order.