Why is Suzaku able to see C.C. through the Knightmare? When Zero (Lelouch) asked for a private meeting with Euphemia, there was a scene where Suzaku was able to see C.C. in the cockpit. C.C. was curious how.

She said, "looks like he can see me [...] is it because of what happened in Narita and Kamine?" Then she said, "or is he also? [...] if that's the case"

What does she mean by "is he also?"?

The way Suzaku saw her is also the same as when C.C. was still inside the tank in the pilot episode.
This was never explained in the anime.
According to show staff they originally had plans to elaborate on Suzaku's connection to geass, but that story point eventually got dropped later on.