Why is Dajjal not mentioned in the Qur’an? And if he isn’t mentioned in the Qur’an where did people get the knowledge about him? And what is the proof that he is real?

Dajjal and all that has been written about him comes from the body of narrations. The Quran alludes to the concept and not the person. Most of the narrations about dajjal are also weak. Most scholars believe that the idea of dajjal is not of one individual but rather an antithesis to the idea of truth.