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 1 fingering below is 6676: 2 fingers, one of them barring the 6th fret, held at the 6th 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.
It leaves out the 3 and 5. 4 strings cannot carry 6 notes, and the 3 is the one this chord can lose without changing what it is.
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♯
abb9
C♯11/G♯
1322
C♯11/B
4324
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.