Actual Guilt: Aside from years of seriously planning to essentially destroy the human race, Kaworu himself hasn't done much of anything. I guess he forced a friend to kill him, though. 8D He's also the reincarnated soul of a creature (Adam) that directly and indirectly killed off half the world's population, melted the ice caps and destroyed the earth's climate. However, Kaworu doesn't really consciously remember any of that, beyond being factually informed that he is Adam.

Mental Guilt: Kaworu doesn't feel all that bad about his attempted murder of an entire species. Uh, definitely not as bad as he should. But he does feel a little guilty over almost accidentally killing Shinji Ikari, who upon entering Landel's is the only human he cares about personally. Kaworu rarely, if ever, analyzes his own actions so guilt isn't an emotion he feels very intensely. It's more like regret. Since Kaworu doesn't actively remember his "past life", he doesn't feel real guilt for what Adam did, besides thinking the event was awfully unfortunate.