Which king of Assyria sent his commander to attack and capture Ashdod in Isaiah 20:1?

Answer: Sargon

Sargon king of Assyria sent his chief commander (KJV: Tartan), who came to Ashdod, attacked it, and captured it.

“Before the year that the chief commander, sent by Sargon king of Assyria, came to Ashdod and attacked and captured it,”— Isaiah 20:1 (BSB)