I've read many posts which almost addressed my question. Problem was none address my exact situation (they were for different versions, classic form design, etc), so none of the answers work for me.
I'm using Nintex 2013 & Sharepoint 2013. I customized the Sharepoint form, using the Nintex Responsive Form template. Not the classic form.
IF user answers Yes, make question A a required field and disable question B
IF user answers No, make question B a required field and disable question A
WHAT I TRIED
When using the responsive forms designer, certain features are unavailable or limited, compared with the standard designer. In the responsive forms designer, I don't see any way to set a rule to accomplish my objective (above).
Best idea I had doesn't seem to work… In SP, I set both questions to be required. In Nintex, I used rules to disable whichever question was no longer applicable. However, the Sharepoint "required" command seems to take precedence. Unless I actually answer BOTH questions, I can't submit the form.
Here's what the form designer and one of the rules lok like, including the only "Then" options available:
your validation formulas should look like