You cannot use focus or focuses in that sentence, because it has several other problems.
You can write something like:
Telepathy is not a suitable topic for a science class, which should focus on ___ and ____.
(By the way, many scientists would tell you that telepathy is a fine topic to discuss or investigate in a science class, and that science focuses on theories as well as "established facts".)
It is not normal to think of a focus "consisting of" something. It makes more sense to say that a focus is something.
The closest thing you could say to your original sentence that would be acceptable to at least some people might be something like
The topic of telepathy is not very suitable for a science class, whose focuses should consist of empirical knowledge and established facts.
The following would be acceptable to more people:
The topic of telepathy is not very suitable for a science class, whose focus should be limited to empirical knowledge and established facts.
It would be ok to use focuses instead of focus. It would also be also ok to use foci instead of focuses.
We can think of one focus being on more than one thing. We can also have more than one focus.