The C minor ninth chord is a 5-note chord consisting of the notes C, Eb, G, Bb and D.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Cm9.
Chords that are a superset of Cm9. The chords include more notes but always C, Eb, G, Bb and D.
Chords that are a subset of Cm9. These contain less notes but all of them are included in Cm9.
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 Cm9 chord. Feel free to save or share the image as needed.