What is the ruling on denying the Emergence of Dajjal?

If he is aware of the Daleel (evidences from the Qur'an and Sunnah) and denies it, then he is a Kafir (disbeliever). This is because he has denied something Mutawatir (reported via mutlitudes of chains of narration) from the Messenger ﷺ. However, if he is ignorant and does not know the Daleel, then the affair must be clarified to him, and if he insists upon denial after that, then he is ruled to be a Kafir. Yes, as he did not believe Allah and His Messenger ﷺ in this matter.