Looks like not all native-speakers know these two words, doesn't it?
Looks like not all native-speakers know these two words, do they?
I'd say this is acceptable, in conversation at least.
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?
It's not really about rules in conversation. Many people use the tag that is appropriate for the thought in their minds, rather than the actual words. Thus:
He has worked in Germany, didn't he?
is wrong by any rule. However, in conversation the speaker might, before he has completed the utterance, answer in his own mind the question 'has he worked in Germany?' with the thought 'Of course he has - he worked there in 2006'. So he adds the tag 'didn't he?' to the unuttered words 'he worked in Germany in 2006'.
I am not suggesting that you do this yourself. I am merely saying that you will hear utterances which are 'incorrect', but which will go unnoticed in conversation.