1)
What is "Yom Nakam"?
1.
Radak: All this is vengeance and payment. Hashem takes vengeance from them and pays what they deserve.
2.
Malbim: Hashem will do so for two reasons. (a) It is vengeance for His own honor - they deny Him and serve idols. This will be in Batzrah. (b) It is the year to pay the quarrel of Tziyon, which they destroyed - this will be in Edom.
2)
What is "Shilumim l'Riv Tziyon"?
1.
Rashi: He will pay those who engaged in quarrel of Tziyon. It cries in front of Him to judge it against those who harm it.
