Can a pious, devout sheikh reveal people's pasts in detail, and is that within his purview, or is it evidence of dealing with jinn?

Your companion is either a charlatan sorcerer who uses jinn to extort people, in which case it is not permissible to deal with him except for the purpose of giving advice; or he is outwardly and inwardly upright and pious, in which case what he does is through a legitimate means, such as a dream. If the dream matches reality, it is truthful; if it contradicts it, it is false. It should not be mentioned or publicized if it involves exposing a person, even if he has given permission, as concealing the faults of a believer is obligatory. Nor should one inquire about such matters. Most people like him are sorcerers who deal with jinn in impermissible ways, and it is obligatory to ascertain his true condition before judging him.