Why did he say "Ko Ya'aseh"?
Malbim: He swore also on the side that his father wants to harm David.
What is the meaning of "Ki Yeitiv El Avi Es ha'Ra'ah Alecha"?
Rashi: If he wants to do evil to you. 1
Malbim: (I will speak bad about you.) If he is pleased to hear bad things about you [this shows that he hates you].
Kli Yakar: Yehonason would not mention bad about David in an absolute way.
Why did he say "v'Galisi Es Aznecha"?
Rashi: If he wants to do evil to you, I cannot send a Shali'ach. I will tell you myself.
What is the meaning of "vi'Yhi Hashem Imach"?
Malbim: I will send you away, even though Hashem is with you.
What is the meaning of "Ka'asher Hayah Im Avi"?
Radak: Hashem will be with you regarding kingship, and help you to overcome your enemies, like He was with my father.
Kli Yakar: When Hashem is with you, I will not be envious. I will be as happy as when He was with my father!
Malbim: He will make you king over Yisrael.