Pharaoh asks, Who is the Lord?
This is not a request for more information about God, but a remark of contempt: why should I listen to the God of these slaves? The people are powerless, so their God must be too. Pharaoh reacts like a dictator who has all the power and listens to no one. The Pharaoh in Egypt was considered a god. He does not accept that people command him, much less a people of slaves!
2 But Pharaoh said, “Who is the LORD, that I should obey his voice and let Israel go? I do not know the LORD, and moreover, I will not let Israel go.”