One nice and simple way for implementing this could be "recently viewed questions" list, where each item would have a pin icon to make them stay on top.
This should, following the android philosophy, be also remembered thourghoutthoughout sessions since a "session" isn't really a concept one should have. This said, a way to unpin all should be provided, since while the system should not have sessions, the user might (very likely, even) still work in sessions, and thus need an option to fall back to a clean slate.