I have heard about people who work with Jinns or have access to them and can find out everything about you. Is this possible and what does Islam say about this matter?
Spying is not acceptable in Islam, whether one is spying with one's physical eyes or using non-obvious/non-ordinary means.
Jinn are not God and cannot know everything, although their unique nature allows them easier access to certain types of information about an individual living person. There is nothing in Islam that precludes the possibility of communicating with jinn, but there is no guarantee that information received in this way is reliable. This is one reason the Qur'an emphasizes that it is from God and not inspiration from jinn (majnun).
It is said in hadith (if I recall, from Imam al-Baqir) that there are jinn who serve the Imams and go to the followers of the Imams and report back to the Imams on their wilayah. Perhaps that is the most important type of finding out about people!
[Of course, the Imams do not require that assistance, but it is related, anyway.]
