guitar chord
C♯11
Six notes in theory; in practice the third is usually dropped, because the eleventh sits a half step above it.
Written the other way round it is D♭11 — the same twelve keys on a piano, a different piece of notation.
Every fingering that fits a hand
x44444
moderate · barre · no 3
x4444x
moderate · barre · no 3, 5
x41102
hard · no 3
999a9b
moderate · barre
x41402
hard · no 3, 5
What is true of it
C♯11 is C♯, E♯, G♯, B, D♯ and F♯ — 1, 3, 5, b7, 9 and 11 counted from C♯.
On an instrument that cannot reach all 6, the 3, 5 and 1 go first, in that order.
The easiest of the 5 fingerings below is x44444: one finger, one of them barring the 4th fret, 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.
3 of the 5 need a barre.
It leaves out the 3. 6 strings cannot carry 6 notes, and the 3 is the one this chord can lose without changing what it is.
1 string stays silent.
Where its notes are on the neck
The brass dots are C♯, the root. Everything else is a chord tone with its degree printed in it.
With a different note underneath
C♯11/E♯
121102
C♯11/G♯
444444
C♯11/B
x21102
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.