The G flat dominant thirteenth chord is a 6-note chord consisting of the notes Gb, Bb, Db, Fb, Ab and Eb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Gb13.
Interactive piano diagram for the G flat dominant thirteenth chord
Reduced chords
Chords that are a subset of Gb13. These contain less notes but all of them are included in Gb13.
G flat dominant thirteenth piano chord chart image
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 Gb13 chord. Feel free to save or share the image as needed.