What they are questioning for among themselves?
What are they questioning
What do they question each other about
Of what do they ask one another
About what (do) they ask/question each other
Are they questioning and…
What are they questioning each other about
What do they question one another about
What is (it) they are questioning about one another
What is that these (disbelievers) are asking one another about
What are they asking (one another)