A teacher is saying this about his student. Is it correct?
I want to know how much can he grasp?
Just a minor point, but neither are questions.
No, neither statement is a question and therefore no question mark, even though a question is indirect and implied and it would possibly generate a response from the listener. If the statement were simply, "How much can he grasp? then, of course, it is question.
Regardless of whether the auxiliary is inverted in the examples and use of a semicolon, it remains an implied question that does not require a question mark. Further, from a grammatical perspective "to know how much can he grasp" qualifies as an infinitive phrase that is the object of "wants". And finally, the sentence structure in the first example, while not terribly bad, is a little awkward.
I want to know; how much can he grasp.
I want to know; how much he can grasp.
Just to confirm, are the sentences above, although a little awkward, both correct?