Short answer
According to a hadith in Sahih Muslim, the Companion Tamim al-Dari met the Dajjal chained on an island in the sea, waiting for permission to come out. Other authentic hadith say he will appear from the east, from a land called Khurasan, and seventy thousand of the Jews of Isfahan will follow him. Where exactly he is now, only Allah knows.
Belief that the Dajjal will appear at the end of time is part of Sunni creed (al-Fiqh al-Akbar). Details such as where he is now come from sahih reports and are accepted as reported, without trying to locate him on a map.
The four schools agree on this.
Explanation
Fatimah bint Qays narrates that the Prophet ﷺ gathered the people and told them what Tamim al-Dari, a Christian who had become Muslim, had seen. Tamim and his companions were shipwrecked on an island, where they met a hairy creature called al-Jassasah and then a huge man bound in chains. He asked them about the unlettered prophet of the Arabs and about places in Arabia, then said, "I am the Messiah, and soon I will be given permission to come out" (Sahih Muslim). He was pleased that Tamim's account matched what he had taught them, and indicated that the Dajjal was toward the east.
Other sahih hadith describe where he will emerge: from a land in the east called Khurasan (Tirmidhi, who graded it hasan); from a path between Syria and Iraq (Sahih Muslim); and seventy thousand of the Jews of Isfahan will follow him (Sahih Muslim).
Some Companions, including Umar, thought a boy in Madinah named Ibn Sayyad might be the Dajjal, and the Prophet ﷺ did not settle the matter at the time. Scholars discussed these reports at length; many relied on the hadith of Tamim as describing the real Dajjal.
Every few years someone online claims to know where he is or who he is. The Prophet ﷺ did not ask us to search for him. He taught us to seek refuge from his trial in every prayer and to learn the first ten verses of Surah al-Kahf. See How can you be protected from the Dajjal? and Who is the Dajjal?
The evidence
Sahih Muslim 2942
Sahih... إني أنا المسيح وإني أوشك أن يؤذن لي في الخروج ...
"I am the Messiah, and soon I will be given permission to come out."
The chained man Tamim al-Dari met was the Dajjal.
Jami' at-Tirmidhi 2237
Grading to be checked... الدجال يخرج من أرض بالمشرق يقال لها خراسان ...
"The Dajjal will emerge from a land in the east called Khurasan."
Where he will appear from.
Sahih Muslim 2944
Sahih... يتبع الدجال من يهود أصبهان سبعون ألفا ...
"Seventy thousand of the Jews of Isfahan will follow the Dajjal."
Describes his followers.
Where the ruling is recorded
- al-Fiqh al-Akbar (Imam Abu Hanifa), Section on the signs of the Hour. Affirms the emergence of the Dajjal as true.
- Sharh Sahih Muslim (al-Nawawi), Kitab al-Fitan, the story of al-Jassasah. Explains the hadith of Tamim al-Dari and the reports about Ibn Sayyad.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.