I’m pretty sure accusative form(the object) of aniga is “ii”, correct me if I’m wrong
As in “wuu ii dharbaaxay”. “Ii” is the object as that is the person who is getting slapped. If I said “waan ku dharbaaxi doona” in this case the person getting slapped is the second person singular accusative form of adiga, the object of the sentence
Unlike English, Somali is rich, complex, and in your example "
wuu ii dharbaaxay" actually means, he slapped him on my behalf.
I think the sentence you were looking for is:
"
Waa uu i dharbaaxay anni", where the 'i' is a preposition denoting position, and '
anni' is the object with the subject implicitly implied in the passive form.
Grammatically, classic Somali, not slang, invariably follows similar pattern as Arabic with variations.
Or so I think.