Can repeated rejections of marriage proposals be caused by an evil eye (ayn), sorcery (sihr), or jinn possession (mass), and how can one know this, and what should I do for God to answer my prayers?

We have no knowledge of the reason for the suitor's turning away from you, nor are we specialized in knowing the symptoms of magic or the evil eye and their treatment. The treatment for these matters is easy through reliance on Allah, perseverance in remembrance of Allah (dhikr), lawful incantations (ruqyah), and supplication (dua), along with having a good opinion of Allah. There is no impediment to proposing marriage to a young man of religion and good character, and do not fear the possibility of his rejection; for the rejection of a proposal is not an indication of a defect or deficiency, but rather it may be due to incompatibility. Rely on Allah and do not despair, for Allah may turn something away from you and reserve something better for you instead.