This is from the movie Harry Potter. Harry and a man, who Harry sees for the first time, are talking, and the man thinks that Harry is aware of his own magical powers - that he is a wizard.
Harry: Excuse me. But who are you?
The man: Rubeus, Keeper of keys and grounds at Hogwarts. Of course you will know all about Hogwarts.
Harry: Sorry, No.
The man: No?
In the second sentence, The man says "Of course, you will know .....". This sentence, at first look, might seem a simple future tense because it has "will" as the auxiliary verb.
But when I think about the meaning of the sentence, it does not seem to be about the future. On the contrary, the man is making a strong guess or a deduction about present. He assumes that Harry already knows that he is a wizard, and he must already have had much information about Hogwarts. So, it seems that "will" here is used to make a deduction.
But, this usage is not so common, so I want to make sure whether the "will" in this sentece is simply a future tense, or is it used for deduction about the present (same as "must")?