How do I request email notification on a question that I did not post whenever a new answer is posted on stackexchange sites?
I don't think that is a supported feature of stackexchange sites. You've got two reasonable ways to track questions.
Mark the question as a favorite (click the star near the voting buttons). When you log back in, you'll see a banner telling you that you have a "favorite" change.
At the bottom of every question page is a little rss symbol and the phrase "question feed". Subscribe via rss to the questions you are interested in. You may even be able to find an Rss->email tool somewhere so that you can get them via email.