The original question had to be edited. Yet, I strongly encourage you to resubmit the second question because it is very effective in terms of illuminating aspects of the work.
The presence of Nazi cruelty is one way in which evil is manifested in Night. The selection process, Dr. Mengele, the gas chambers, as well as the punishment that the Nazis inflicted on their targets are all examples of how evil is manifested. The Nazi manifestation of evil is seen at different points in the narrative. Consider when Moshe the Beadle was deported:
The train had stopped. The Jews were ordered to get off and onto waiting trucks. The trucks headed toward a forest. There everybody was ordered to get out. They were forced to dig huge trenches. When they had finished their work, the men from the Gestapo began theirs. Without passion or haste, they shot their prisoners, who were forced to approach the trench one by one and offer their necks.
Following this is the image of infants being used as "target practice." Another example of the Nazi manifestation of evil would be seen in Eliezer's first night in the camp:
An SS came toward us wielding a club. He commanded:
"Men to the left! Women to the right!"
Eight words spoken quietly, indifferently, without emotion.
Eight simple, short words. Yet that was the moment when I left my mother.
There is a dehumanizing reality to this manifestation of evil. It is one in which human beings are devoid of humanity, both aggressors and victims.
However, Wiesel's work is successful in showing how evil is manifested amongst the victims of the Holocaust, as well. For Wiesel, the true horror of the Holocaust is how the patterns of dehumanization that the Nazis inflicted on their targets were replicated by the targets themselves. In doing so, there is humanity denied, collectivity withered, and solidarity absent.
This manifestation of evil is seen with Moshe the Beadle returning to Sighet, only to be discredited and silenced. It is also seen with Madame Schachter, being beaten and silenced on the train for her visions. This same manifestation of evil is evident in how the prisoners no longer see one another as human beings, but rather as obstacles to survival. Consider the point in the narrative where a father steals bread for his son, who in turn beats his father for the bread. The son is then beaten by two men because they want the bread he has stolen. Father and son lie as corpses together, but also as a reminder of how evil manifested himself amongst the targets of the Nazi cruelty. Rabbi Eliahu's son leaving his father behind and Akiba Drumer's sad request of reciting Kaddish for him denied are also examples of how evil is manifested amongst those who were the targets for the Nazis. In this, evil is shown as being universal, and the sad legacy that all of us inherit from the Holocaust.