To which Resha'im does this refer?
Rashi: To Esav - "v'Nasati Es Nikmasi be'Edom b'Yad Ami Yisrael" (Yechezkel 25:14).
Radak: It is all Resha'im; kingship will remain only with Yisrael. So Daniel interpreted Nebuchadnetzar's dream (Daniel 2:44).
Who will cut off the horns?
Rashi: Yisrael will cut off the horn of Amalek.
Radak: Yisrael will cut them off in the war of Gog and Magog.
Malbim: Straightness will cut them off.
Whose horns are "Karnos Tzadik"?
Rashi: They are the horns of the Tzadik of the world, Yisrael - they are Hashem's praise.
Radak: Tzadik is Yisrael, who are the Tzadik of the nations.
Malbim: This is the straightness planted in people. They will recognize Hashem's honor and greatness, and learn to do Tzedek and straightness.