What exactly was Pharaoh asking (or 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."
Oznayim la'Torah: 'Who is Hashem that I should obey even the smallest request of His, and even if I knew Hashem, I would not carry out such a major request!'
What was Hashem's reaction to Pharaoh's declaration, "Mi Hashem ... "?
Sanhedrin 94b: Because Pharaoh personally blasphemed Hashem when he declared "Mi Hashem," Hashem personally punished him at the Yam-Suf, where the Torah writes "va'Yena'er Hashem Es Mitzrayim b'Soch ha'Yam" (14:27). 1
Chulin 89a: 'I yearn for you (Yisrael -- says Hashem -- ), because even when I bestow greatness upon you, you make yourselves small; But the nations of the world do not do that - I bestowed upon Pharaoh greatness, and he declared "Who is Hashem?"
Torah Temimah: Not like Sancheriv, who blasphemed Hashem via a Shali'ach, and whom Hashem therefore punished via a Shali'ach.
What is the gist of the second half of Pharaoh's response, "Lo Yada'ti Es Hashem... "?
Seforno: I never heard of a being who can create something out of 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.
Which is apparently one of the connotations of the Name Havayah.
