"Is he asking you?"
Translation:O sana mı soruyor?
It is the difference between the direct object and the indirect object. In English, we gloss over the difference with a verb like "ask" -- but really you ask a question/inquiry [direct object] to a person/resource [indirect object]. The question can have the accusative case (or not, if it is not a specific/definite d.o.), but the person-the-question-is-directed-to will have the dative case.
Is he asking you the question? = O sana mı soruyu soruyor?
Is he asking you questions? = O sana mı soru soruyor?