The B sixth chord is a 4-note chord consisting of the notes B, D#, F# and G#.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as B6.
Chords that are a superset of B6. The chords include more notes but always B, D#, F# and G#.
Chords that are a subset of B6. These contain less notes but all of them are included in B6.
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 B6 chord. Feel free to save or share the image as needed.