The G flat major thirteenth chord is a 6-note chord consisting of the notes Gb, Bb, Db, F, Ab and Eb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Gbmaj13.
Interactive piano diagram for the G flat major thirteenth chord
Chords that are a subset of Gbmaj13. These contain less notes but all of them are included in Gbmaj13.