How can I know whether someone I know is a jinn or a shapeshifting devil, and what should be recited from the Quran or elsewhere to uncover that and avoid its evil?

Jinn can take on various forms, such as dogs, cats, humans, and snakes, especially black dogs and cats, because blackness has a strong ability to gather satanic forces. Jinn cannot harm anyone except by Allah's permission, and it is impossible to distinguish a jinn in human form from a human being. To protect oneself from them, one should maintain regular remembrance of Allah (dhikr), recite Ayat al-Kursi, and the concluding verses of Surat al-Baqarah. Among the benefits of Ayat al-Kursi is that it provides a protector for its reciter, and no devil will approach him until morning. There are multiple stories narrated about the Companions (Sahabah) and jinn in various forms who guided them to Ayat al-Kursi for protection. Such incidents are rare, and one should not fall into doubts and assume that those around them are jinn in human form.