How do you play a C diminished added 9th chord

It would depend on the diminished chord. Diminished, half diminished or diminished 7th? Either way, whichever one you use you’d need to simply add the 9th, which for the key of C will be D. Here’s one way for each chord, to be honest, about the only easy way I could find without omitting a note.

C dim /9

E: 2
B: 4
G: 5
D: 0
A: x
E: x

C half dim/9 (or Cm9b5)

E: 6
B: 4
G: 5
D: 4
A: 5
E: x

Cdim7/9

E: 5
B: 4
G: 5
D: 4
A: 5
E: x