The G flat major seventh chord is a 4-note chord consisting of the notes Gb, Bb, Db and F.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Gbmaj7.
Chords that are a superset of Gbmaj7. The chords include more notes but always Gb, Bb, Db and F.
Chords that are a subset of Gbmaj7. These contain less notes but all of them are included in Gbmaj7.
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 Gbmaj7 chord. Feel free to save or share the image as needed.