A dominant 9th chord (usually just called a ninth chord) is created by adding a 9th degree to any dominant 7th chord. For example, a C9 chord contains the notes C, E, G, Bb and D (1, 3, 5, b7 and 9). Here are some common open ninth chord shapes.
C9
Db9
D9
Eb9
E9
F9
G9
F#9
Ab9
A9
Bb9
B9