The B dominant ninth chord is a 5-note chord consisting of the notes B, D#, F#, A and C#.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as B9.
Chords that are a superset of B9. The chords include more notes but always B, D#, F#, A and C#.
Chords that are a subset of B9. These contain less notes but all of them are included in B9.
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 B9 chord. Feel free to save or share the image as needed.