I heard the high thin laugh again. “You’re nobody, son. You don’t
exist – can’t you see that? The white folk tell everybody what to
think – except men like me. I tell them; that’s my life, telling white folk how to think about the things I know about. Shocks you,
doesn’t it? (Ralph Ellison, Invisible Man)
Which is the semantic subject of the verb think, the white folk or everybody?
The subject is the “main” part of a clause. The other part of a clause (the predicate) should be telling you something about the subject. In active voice, the subject of a verb will always be the thing that is verbing.
In this statement you have a nested clause, which seems to be what’s causing you the confusion.
The white folk are always telling everybody [what to think].
The verb think is not directly linked to the subject of the main clause (white folk). Rather all that follows is its predicate, and to tell is the verb tied to white folk. The bracketed section of the sentence is the nested clause.
So the verb think is in the nested (or subordinate) clause, of which white folk is no longer the subject. The thinking is being done by everybody in this sentence — grammatically speaking, at least.
The subject of the verb think is everybody.