In the days of which king of Judah did the word of the LORD come to Zephaniah?

Answer: Josiah

Zephaniah prophesied in the days of Josiah son of Amon, king of Judah.

“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)