Jack seriously had no idea Kanji was this innocent. Mainly because their conversations have already encompassed crushes on cross-dressing friends and coming out as gay, and in his experience those things usually come after learning about the facts of life, not before.
However. Kanji isn't shying away from this, even though it's clear he's not altogether comfortable, and so he's determined to do this right.
"You don't actually know anything about sex?" he asks, because it'll help if they're both on the same page here.