"Don't kill him yet!"
Then that other exercise was wrong. If you find it, let us know where it is, please. (I can't find it right now.)
Also, Wej does not exist in Klingon; there is no capital W in the language.
wej already means "not yet", so wej yIHoH is "don't kill him yet".
wej yIHoHQo' would mean something like "don't not kill him yet", if it meant anything at all.