Could you explain the usage of it in the following sentences?
- I don't like it when you speak like this.
- I hate it when you speak like this.
- I know it for certain that he is in town now.
- He owes it to his brother that he became a research chemist.
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(1) and (2) are a different construction from (3) and (4).
Note that the subordinate clauses in the first two are adverbial and can be preposed
The it in these sentences is referential, an indefinite direct object required by the transitive verbs like and hate. The position of the clause is irrelevant.
(3) and (4) are not adverbial clauses, but extraposed complements, as @Araucaria says. The it in this case is the usual dummy it of Extraposition. It's unusual that Extraposition is applied to direct objects instead of subjects. Indeed, I find (3) with it ungrammatical, but just fine without it; YMMV, of course. But (4) is fine, in fact almost unavoidable, given the complex set of presuppositions involved.
Sometimes it is difficult to processs a clause when it functions as the Complement of a particular type of verb. Other times, we want to delay the Complement of the verb when it is a clause to give it greater prominence at the end of the sentence. In both such circumstances, we use the dummy pronoun it as the Complement of the verb and shunt the smaller clause down to the end of the sentence where it appears as an Extraposed Complement.
The Original Poster's sentences could be paraphrased like this:
Whether the when-strings there are clauses or not is a bit controversial, but they definitely work the same way as clauses.