Below are some ideas / reference material for soloing over a C altered dominant chord. Wherever "pentatonic" is indicated, I am refering to a "minor pentatonic".

I will break the altered chords into 2 groups: C7b5b9 and C7#5#9. I'll try not to confuse anyone here....to figure out which of the two groups any altered chord belongs to - if the chord contains *either* a #5 or a #9, it goes in the second group - it doesn't have to contain both tensions. You *can* play material containing a b9 over chords from the second group. In fact, depending on what you want to achieve sound-wise - try anything!

C713b9, C7b9

C half-whole diminished scale
Bb melodic minor

Triad Superimposition

F# major - contains b9 and b5
A major- contains b9

C7#5#9

C "altered" scale or super-locrian (Db melodic minor)
Bbm7b5 arpeggio
C whole tone scale
C, E and G# augmented triads

Pentatonics