Final answer:
The sentence given is a compound-complex sentence with two main clauses and one subordinate clause.
Step-by-step explanation:
The structure of the sentence "Did you know that some people don't do their reading assignments?" is a compound-complex sentence. It contains two main clauses: "Did you know?" and "some people don't do their reading assignments." The subordinating conjunction "that" introduces the subordinate clause "some people don't do their reading assignments."