Hi, teachers:

Can you tell me which one of the following sentences is correct? (The focus here is the "tags" following each question, which is one of my big weaknesses.)

Looks like not all native-speakers know these two words, doesn't it?
or should it be:

Looks like not all native-speakers know these two words, do they?
or
Looks like not all native-speakers know these two words, don't they?
Any rule to follow when the preceding sentence is a composite sentence?