1)
How did Yonadav know that he killed only Amnon?
1.
Rashi: Avshalom placed this on his servants to kill Amnon from the day he raped Tamar. Malbim - the one who saw that he killed Amnon thought that Avshalom wants to inherit the kingship. If so, he would kill all Bnei ha'Melech! This was not his intent; he only wanted to avenge the rape of Tamar.)
2)
What is the meaning of "Sumah"?
1.
Radak: [The act of killing Amnon] was placed [in his mouth; he was always talking about Amnon's evil from the day he raped Tamar].
2.
Radak citing Targum Yonasan: It was hidden [in his heart]. He similarly translated "Asher Sam Lo ba'Derech" (1:15:2) 'he hid in ambush.'
