The D flat diminished chord is a 3-note chord consisting of the notes Db, Fb and Abb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Dbdim.
Chords that are a superset of Dbdim. The chords include more notes but always Db, Fb and Abb.
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 Dbdim chord. Feel free to save or share the image as needed.