Is it obligatory for a Muslim to emigrate from a country where Shiites are numerous and there isn't a single Sunni?

First, a Muslim must adhere to the path of Ahl al-Sunnah wal-Jama'ah (the People of the Sunnah and the Community), for it is the path to salvation.

Second, one must be gentle with parents, advise them with wisdom, and pray for their guidance.

Third, if you have the ability and knowledge to establish the Sunnah, invite to it, and forbid evil in an environment of innovation (bid'ah), then remaining there is permissible and may be a cause for great good. However, if you fear for yourself fitnah (temptation/tribulation) or harm, or if you cannot openly practice your religion, then it is better to migrate to the lands of Ahl al-Sunnah; because remaining in a place where one witnesses evil is itself evil and may necessitate contentment with it. Some scholars have made migration obligatory from places where innovation is widespread and the Salaf are reviled.