I don't think that there are many instances where there is tremendous dignity in the face of cruelty in the narrative. Part of this lies in Wiesel's design to show that the real horror of the Holocaust is how the Nazis took the humanity of their victims, revealing a cycle of abuse. The Nazis dehumanized their victims and the victims dehumanized one another in a sick, replicate cycle of inhumanity. I would say that one particular moment where dignity is evident would have to be in the moment when Eliezer is savagely beaten by Idek. The beautiful French girl that has seen Eliezer often but not spoken because of perceived language barriers, helps him in this moment. She tends to him, stopping his bleeding, and feeds him. In a moment where there is absolute and pure savagery, there is an instant of humanity a moment of redemption. This is critical in the narrative and it represents an instant where dignity is evident. It is a moment where the Nazis actually were defeated in not being able to take the dignity of all of those who they oppressed. As mentioned, there are not many examples of this, reflecting the scale of the Nazi crimes, but this moment is one in which there is dignity in the face of inhuman cruelty.
In Chapter 6, Eliezer recalls seeing Rabbi Eliahou's son running by his side and realizes that Eliahou's son was trying to leave his father behind. The rabbi's son felt that his father was becoming weak and wanted to get rid of him. Rabbi Eliahou's son believed that he had a better chance of survival without having to care for his exhausted father. Eliezer is disgusted at the boy's decision to leave his father behind and prays that he will never abandon his father. In Chapter 8, Eliezer's father becomes extremely sick and is on the verge of dying. When the soldiers inhumanly refuse to give Eliezer's father food, Eliezer demonstrates his dignity by giving his father the rest of his soup. Eliezer continues to feed and care for his father despite the advice from other prisoners. Eliezer's selfless gesture demonstrates his dignity. Eliezer does not become like Rabbi Eliahou's son and refuses to abandon his father in a time of need.