Edit: This is wrong.
But you can always turn it into a reflexive verb:
"Kan du forklare meg hvorfor himmelen er blå?"
That's not reflexive, "meg" is an indirect object in your example, and the agent and beneficiary ("du" and "meg") are two different people.
I translated as "He must make himself clear". I would think the meaning is the same, and you see klar (clear) in forklare.
Does the "forklare seg" have multiple meanings as it does in English?
That is, does it imply:
"He must be the one to do the explaining"?
"He has done something and must explain his actions"?
- Can it be either depending on context? ?