YOU SAID:

If only I knew what he was up to

INTO JAPANESE

彼が何をしているのか私が知っていれば

BACK INTO ENGLISH

If I knew what he was doing

INTO JAPANESE

彼が何をしているのか知っていたら

BACK INTO ENGLISH

If you knew what he was doing

INTO JAPANESE

彼が何をしていたか知っていれば

BACK INTO ENGLISH

If you knew what he was doing