The G sixth chord is a 4-note chord consisting of the notes G, B, D and E.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as G6.
Chords that are a superset of G6. The chords include more notes but always G, B, D and E.
Chords that are a subset of G6. These contain less notes but all of them are included in G6.
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 G6 chord. Feel free to save or share the image as needed.