"What day is today?"
Translation:Leo ni siku gani?
Nini is only used on its own. You can't use it with a noun. You can't say
siku nini for "what day".
What did you watch? = Ulitazama
movie did you watch? = Ulitazama
Some old prescriptivists would say that "what date" is incorrect in English too and would insist on "which", but that's just silly. English has moved on.