Looks like C.C. will remain C.C. to us. According to Pash! vol. 09, we'd learn her true name in this ep, but Taniguchi chose to blank out the part where Lelouch says her name. So, in short, only those who are good at reading lips will know.
It seems that Taniguchi wants to preserve the veil of mystery shrouding C.C. We nevertheless get to see her past as a consolation - the part with her in that nun outfit (or was that an earlier avatar of hers - or the original C.C.?).