Which king prayed, "We do not know what to do, but our eyes are upon You"?

Answer: Jehoshaphat

Facing a vast army, Jehoshaphat confessed that Judah was powerless and looked to God. The LORD answered through Jahaziel.

“Then Jehoshaphat stood in the assembly of Judah and Jerusalem in the house of the LORD in front of the new courtyard”— 2 Chronicles 20:5 (BSB)