Guitar chords in the key of C major:
C Dm Em F G Am Bdim

Chord Cmaj9 notes: C, E, B, D and E. You should not play the 6th string.

The string 1 (E) is left open.

C major 9th guitar chord's alternative names: Cmaj9, CM9, Cmaj7(9).

Steps: 1-3-5-7-9.
1(C), 3(E), 5(G), 7(B), 9(D).