Is it obligatory to ask the needy person about his prayer when expiating by feeding, or is the apparent taken into consideration?

The person giving the expiation food is not required to inquire whether the poor person receiving it prays or not. The fundamental principle is that a Muslim should maintain their prayers. Even if it is confirmed that they do not pray, the disbelief of one who abandons prayer is a matter of scholarly disagreement. The preponderant opinion is that it is a minor disbelief (kufr dūna kufr), not one that expels a person from the faith. Therefore, there is no impediment to giving expiation to a poor person who does not pray, provided they are indeed poor, though righteous individuals are more deserving.