in Stackoverflow, I happen to just post a comment on someones question; yet whenever that question is updated or receives answers or comments, I don't get any warning whatsoever. How do I activate that or manage those questions?
You can favorite that question so that whenever there are any updates to it, you'll be notified regarding that. This is the most you can get out that because there is no such facility on SE to subscribe a question for any updates on it, as of now.
You can read "How do favorite questions work?" for a more detailed information on it.