Zexion will be in her Illusions class and will play dumb about how exactly he does his illusions, definitely not saying anything about his lexicon if he can avoid it.

He'll be very curious about how the other students perform, probably too curious, but he'll claim its only because he wants to know in case their powers work similarly to his own. It's a lie, he's busy scheming away, but he'll play innocent in the matter.