The E flat diminished seventh chord is a 4-note chord consisting of the notes Eb, Gb, Bbb and Dbb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Ebdim7.
Chords that are a subset of Ebdim7. These contain less notes but all of them are included in Ebdim7.
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 Ebdim7 chord. Feel free to save or share the image as needed.