The G flat eleventh chord is a 5-note chord consisting of the notes Gb, Db, Fb, Ab and Cb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Gb11.
Chords that are a superset of Gb11. The chords include more notes but always Gb, Db, Fb, Ab and Cb.
Chords that are a subset of Gb11. These contain less notes but all of them are included in Gb11.
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 Gb11 chord. Feel free to save or share the image as needed.