Praise be to Allaah.
It is not permissible to seek the help of the jinn in finding about what the problem is and how to treat it, because seeking the help of the jinn is shirk. Allaah says (interpretation of the meaning):
“And verily, there were men among mankind who took shelter with the males among the jinn, but they (jinn) increased them (mankind) in sin and transgression”
“And on the Day when He will gather them (all) together (and say): ‘O you assembly of jinn! Many did you mislead of men,’ and their Awliyaa’ (friends and helpers) amongst men will say: ‘Our Lord! We benefited one from the other, but now we have reached our appointed term which You did appoint for us.’ He will say: ‘The Fire be your dwelling place, you will dwell therein forever, except as Allaah may will. Certainly your Lord is All-Wise, All-Knowing’”
The meaning of the phrase ‘We benefited one from the other’ is that the men venerated the jinn and submitted to them and sought help from them, and the jinn served them by doing what they wanted and bringing them what they asked for. That includes informing them of the type of sickness and its causes, because the jinn can come to know of things that humans cannot; but they may tell lies, because they cannot be trusted, and it is not permissible to believe them. And Allaah knows best.