The B suspended fourth flat ninth chord is a 5-note chord consisting of the notes B, E, F#, A and C.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Bb9sus.
Chords that are a superset of Bb9sus. The chords include more notes but always B, E, F#, A and C.
Chords that are a subset of Bb9sus. These contain less notes but all of them are included in Bb9sus.
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 Bb9sus chord. Feel free to save or share the image as needed.