I live in Japan. Theres a lot of disbelievers here and in daily life situation; there are times which I do sports and my friends touch me. Now I don’t have Yaqin (certainty) on which religion they follow, but I mostly assume they are atheists since most of them are like that. Now sometimes when they touch me or most of the times, they are wet. And the sweat of disbelievers are Najis. Is my wudu batil, and my prayer too if I don’t wash the part on which they touched me and I pray? Also do I have to ask their religion? And what if I know they are kafir (and they have touched me with their wet hand) and I pray. Is my prayer sahih wether it be wajib prayer or mustahb?

1- Your wudhu is not Batil
2- However, if they touched with a wet hand and you are confident that they are not from the People of the Book, then you must wash the area they touched before you pray. Deliberately not washing the area before prayer invalidates the prayer.