The infix might change depending on what the object was, right? For example if we were taking about an onion, it would read "usikipike."
Correct! All variants should be accepted. :)
This particular course is really badly done....no context for many of the object markers
It really should be improved.
It would be nice if in this lesson all examples have a noun as object so we can properly practice the correct conjugations for each noun class
Just remember that this is only one of the variants. It could be
usikipike (kiazi) etc
Is this a negative imperative? So in this case we have both subject and object infixes?
Yes, u- is the subject prefix and -si- is the negative and -i- is the object infix.