How to display unanswered questions when using the Answers module?
The demo site related to the 7.x.-4.x version of the Answers module uses a further enhanced version of the most recent dev release. Some of the views have been enhanced and will be pushed to D.O soon. These views are available already in Views Export format via files attached to comment #5 in issue #2783513).

The (new) view related to the questions has a tab titled "unanswered", which contains the list of all questions that are "unanswered".

So to actually answer your question, I suggest you experiment a bit with the updated view of questions as contained (in export format) in the issue mentioned above.

Disclosure: I'm a co-maintainer of this module.