Zephaniah 1:1 traces the prophet's family line back four generations to whom?

Answer: Hezekiah

Zephaniah was son of Cushi, son of Gedaliah, son of Amariah, son of Hezekiah (KJV: Hizkiah).

“This is the word of the LORD that came to Zephaniah son of Cushi, the son of Gedaliah, the son of Amariah, the son of Hezekiah, in the days of Josiah son of Amon king of Judah:”— Zephaniah 1:1 (BSB)