One of the first feedback I received for creating surveys is that adding answers/subquestion doesn't seem very obvious and could be more intuitive.

But the easiest addition to help point the user to this when they click "save",
apart from possibly seeing the warning notice (in small print) that "You need to add answer options to this question", would be to simply add a quick actions button for this :)

The buttons may be visually more obvious than the navigation menu amongst many other options as well as small print warning message and thus would probably help a lot of users to find where/how to add answer options.

FYI
I will submit a separate feature suggestion for answer options to become available for input within the question itself, like it is with other platforms and one would naturally expect (that is if this is possible).
As well as one suggestion to add a button in the "List questions" view (next to preview, edit and summary).