What exactly was Pharaoh asking (saying) in the first half of his response?
Rashbam: "Who does Hashem think He is that I should obey Him to release Yisrael, My slaves, from my land to worship Him? What rights does He have over this people that they should worship Him?
Targum Yonasan: The Name of Hashem is unknown to me that I should be obligated to obey Him to release Yisrael! I did not find the Name Hashem in the catalogue of deities.
Moshav Zekenim: If Hashem were upset that Yisrael are here, He would have revealed Himself to me. He did so for one night that Avimelech kept Sarah. All the more so He should do so for all of Yisrael! Targum Onkelos supports this - "Lo Isgeli Li."
What is the gist of the second half of Pharaoh's response?
Seforno: I never heard of a being that creates when there is absolutely nothing; 1 and even if there is such a being, I will not release Yisrael!
Targum Onkelos: The Name of Hashem is not known to me, neither will I release Yisrael!
Targum Yonasan: I am not afraid of Hashem, neither will I release Yisrael.
One of the connotations of the Name Havayah is that He creates out of nothing.