In the temple of which god was Sennacherib killed by his sons?

Answer: Nisroch

While worshiping in the temple of his god Nisroch, Sennacherib was killed by his sons Adrammelech and Sharezer.

“So Sennacherib king of Assyria broke camp and withdrew. He returned to Nineveh and stayed there. One day, while he was worshiping in the temple of his god Nisroch, his sons Adrammelech and Sharezer put him to the sword and escaped to the land of Ararat. And his son Esar-haddon reigned in his place.”— 2 Kings 19:36-37 (BSB)