which one is correct 3?

i think "the coursework of some students" is better (omit "of the"). although "some of the students" is correct, adding "of the" would make the sentence too clumsy.

I think "coursework" is an uncountable noun while "student" is countable.
We can put an "s" after "student" to describe more than one.

So, I would say "the coursework of some of the students" is correct.
However, "The coursework of some students..." is better and simpler.

just depend-on how many coursework that you have, if only one, it should be: "the coursework of (for) some of the students", if more than one, it should be: "the courseworks of (for) some of the students"

the coursework of some of the students 才是對的