The C sharp major thirteenth chord is a 6-note chord consisting of the notes C#, E#, G#, B#, D# and A#.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as C#maj13.
Interactive piano diagram for the C sharp major thirteenth chord
Reduced chords
Chords that are a subset of C#maj13. These contain less notes but all of them are included in C#maj13.
In case you prefer a non-interactive variant of the chord chart, we've embedded a PNG image below that shows
the notes for the the C#maj13 chord. Feel free to save or share the image as needed.