How can someone afflicted by the evil eye or envy confirm their affliction, what are the most prominent signs indicating it, how can they treat themselves independently, and what is the sin of those harmed by evil people?

We do not have definitive proof to ascertain whether a person is afflicted by envy. However, one can seek help from some experienced practitioners of Ruqyah (Islamic exorcism). As for the wisdom behind the existence of the evil eye, it is one of the trials that Allah has placed in this world. Allah Almighty said: "And We have made some of you [means of] trial for others - will you have patience? And your Lord is ever Seeing." [25:20] The Islamic Ruqyah for the evil eye and other afflictions has been previously explained.