What is "Oy l'cha Mo'av" referring to?
Rashi: It refers to Bil'am's curse of Mo'av
See Sifsei Chachamim.
What is the meaning of "Am K'mosh"?
Rashi and Ramban: It means the people of K'mosh, the god of Mo'av (to whom the people were totally devoted
Who turned Mo'av's sons into refugees and its daughters captives?