أَفَأَصْفَاكُمْ رَبُّكُمْ بِالْبَنِينَ
Has your Lord singled you out for sons?
The verse challenges an inconsistent belief: preferring sons for oneself while attributing daughters to God. The rhetorical interrogative performs denial and rebuke by exposing the contradiction.
No unknown information is being requested. The force is to reject an untenable division; surrounding context is necessary to see why the literal question is not the intended message.