"Yes, I do know that." "Yes, I did know that." ("Did knew" is an impossible combination: only one past tense per statement allowed.)

yes, i know. yes, i knew.

PRESENT: I know (now) his name. PAST (some): The minute I saw him I knew (past) his name. I knew his name at the time but I don't know it now. I did know (past) his name once upon a time. - maybe I have since forgotten