The D suspended second chord is a 3-note chord consisting of the notes D, E and A.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Dsus2.
Chords that are a superset of Dsus2. The chords include more notes but always D, E and A.
Chords that are a subset of Dsus2. These contain less notes but all of them are included in Dsus2.
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 Dsus2 chord. Feel free to save or share the image as needed.