9th sus4 chords
The ninth suspended chords are less common than the regular sus4 and sus2 as well as the 7sus4. The 9th sus chord is almost similar to the dominant 9th chord, but in many cases the fingerings are unnatural to play. In general, it's hard to find any fingerings that include open strings for this chord category.
The diagrams below are suggestions of how to play these chords (see also additional versions, including movable shapes, further below).
The 9sus4 is built with five notes, but at least one note is often left out, making it a four-note chord.
Notice that D9sus4 also can be barred over all strings (555555), which makes it an inverted version, D9sus4/A that is.
A, quite peculiar, open position option for A9sus4 is X00000.
Open position alternatives for these chords are mostly found when the root is not the bass note. Notice that some of these version will not underline the character of the chord very well.
9th suspended chords with flats and sharps
Since these are not played all that often, they are only presented in shortened notation:
C sharp / D flat 9sus4: X44444
D sharp / E flat 9sus4: X66666
F sharp / G flat 9sus4: XX4454 / 2X2100
G sharp / A flat 9sus4: XX6676
A sharp / B flat 9sus4: X11111
Two moveable shapes for this chord category are C9sus4 as X33333 and 8X8766.
The ninth suspended fourth is built with the formula 1-4-5-b7-9.
Progressions including this chord type:
G9sus4 - G7 - F7 - C7
Em - Am - D9sus4 - D7 - G
D - Dmaj7 - D6 - D - A9sus4 - A7 - D
In the famous song "California Dreaming" a 9sus4 to 7th change is used:
Am - G - F - G - E9sus4 - E7 (capo 4)
No, this chord type cannot exists since the 9th interval and the 2nd interval are the same note.
C7b9 and C7#9 compared to C9sus4
The C9sus4 formula 1-4-5-b7-9 are quite similar with both C7b9 (a 1-3-5-b7-b9) and C7#9 (a 1-3-5-b7-#9).
11th and C9sus4 relationship
Even more related are the dominant 11th, which actually can be seen as the same chord as the suspended ninth. This can be seen in the comparison between C9sus4 with the notes C - F - G - Bb - D and C11 with the notes C - E - G - Bb - D - F. The only difference is theoretical, in regards of the slightly altered note order.
Alternative chord names
C9sus4 is theoretically identical with Bb/C, C#9sus4 is theoretically identical with B/C# and so on.