Custom question sets cannot be directly exported, however they can be manually copied and pasted from a web browser.
By default, custom question sets can be found in the following location:
C:\Users\<user>\Documents\My MindGenius Templates\Questions
(You can also access the default question sets at : C:\Program Files (x86)\MindGenius\V7*\Templates\Questions)
You can then right click the question set you want to copy, select "Open with", then select your web browser.
*Change V7 to the version of MindGenius you're currently using if required