Q: WHAT YEAR DID JOTHAM BEGIN HIS REIGN IN JUDAH?
A: IT DEPENDS WHAT CALENDAR YOU ARE USING!
On the Gregorian calendar (the one you might have on your wall) the year was 691 BC.
On the Hebrew calendar, sometimes called the biblical calendar, the year was 3356 AM.
2 Kings 15:32-33 – In the second year of Pekah the son of Remaliah king of Israel began Jotham the son of Uzziah king of Judah to reign. Five and twenty years old was he when he began to reign, and he reigned sixteen years in Jerusalem. And his mother's name was Jerusha, the daughter of Zadok.