The B dominant thirteenth chord is a 6-note chord consisting of the notes B, D#, F#, A, C# and G#.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as B13.
Chords that are a subset of B13. These contain less notes but all of them are included in B13.
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 B13 chord. Feel free to save or share the image as needed.