The B flat minor eleventh chord is a 6-note chord consisting of the notes Bb, Db, F, Ab, C and Eb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Bbm11.
Chords that are a subset of Bbm11. These contain less notes but all of them are included in Bbm11.
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 Bbm11 chord. Feel free to save or share the image as needed.