Do you have access to the tips & notes? The ones for the Object Infix lesson explain all this (infixes and prefixes are the same, with the exception of me/you/(s)he/etc). I ask because you've queried this sort of thing a number of times.
What about gani though? Could you simply use mkono gani unauma? Without always having to adjust to the noun class?
I unterstand it's good to learn this form here but just generally, isn't gani the more common way to express "which"?