There are many important events that could be pointed out, but I would go with the following six because of their importance to the development of the themes in the book.
1. Elie is separated from his mother and sisters (as the men are split from the women).
2. Elie lies about his age so he can stay with his father.
3. Elie sees babies being thrown into a flame.
4. Elie walks in on Idek the Kapo while he is with a girl and receives 25 lashes with the whip.
5. Elie watches the hanging of a boy with "an angelic face". For thirty minutes the boy writhes as a stranger asks "Where is God now?" and Elie replies "He is hanging here on the gallows".
6. Elie injures his foot and is sent to the hospital to recover.
I think that you can find many different answers to this question. I would also suggest that there is no substitute than reading over this section of Wiesel's narrative because the main events that transpire might be what is within Elizer's mind. It is extremely important to not trivialize or to undervalue the notion of internal reflection in the text, and particularly, in this section of the text. Within this section of the text, I would focus on Elizer begins the process of rejecting the notion of faith and redemption with what is seen on the first night at Birkenau when Elizer sees men, women, and children being burned alive at the hands of the Nazis. I would also focus on the level of dehumanization that presents itself, such as Eliezer being branded with a number and the cruelty that exists all around Elizer, such as the beatings of Idek and their effect on Eliezer. At the same time, I think that it might be important to discuss how Eliezer is losing the sense of connection to others, such as losing the ability to care for his father as well as the feelings experienced once the child who wanted extra soup is hung from the gallows. In the end, I think that one can determine many events from this section that could be considered "main events," but there is no denying the fact that the Eliezer's internal rumination underscores it all.