The G flat minor thirteenth chord is a 6-note chord consisting of the notes Gb, Bbb, Db, Fb, Ab and Eb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Gbm13.
Chords that are a subset of Gbm13. These contain less notes but all of them are included in Gbm13.
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 Gbm13 chord. Feel free to save or share the image as needed.