What is the ruling on a teacher giving his sister's son potential exam questions, knowing that he is unsure whether they will be the exact same questions, and what are the consequences if he is mistaken?

If the exam questions are authorized for publication, there is no harm in the teacher giving them to a relative or anyone else, and this is not considered cheating. However, if the teacher knows or strongly suspects that their publication is prohibited, then giving them out is considered a betrayal and cheating, and he must repent. If the teacher did not know this and then his error became clear, there is no sin upon him, for Allah Almighty says: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended. And ever is Allah Forgiving and Merciful."