The E minor sixth chord is a 4-note chord consisting of the notes E, G, B and C#.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Em6.
Chords that are a superset of Em6. The chords include more notes but always E, G, B and C#.
Chords that are a subset of Em6. These contain less notes but all of them are included in Em6.
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 Em6 chord. Feel free to save or share the image as needed.