1)
What is "ba'Shevi'i"?
1.
Radak: It is Tishrei, the seventh month.
2)
What Korbanos will they offer then?
1.
Radak: They will offer the same Korbanos during the seven days of Sukos like they offered during Pesach 1 . Also this will be a Chidush - the Torah specified a different Korban for each day of Sukos! Here it does not specify a Korban for Shemini Atzeres; perhaps it will be like the Torah said.
1
Malbim: Also the Minchah and oil will be the same as during Pesach. The days of Chinuch will extend from Pesach until Shemini Atzeres. The war of Gog and Magog and the end of the salvation will be during Sukos, like it says in Zecharyah Perek 14.
