Dehumanization is shown when the Jewish people were threatened on the train and were told if one of them runs the rest will "be shot like the dogs they are."
Another would be when Elie is tattooed with his identification number and is robbed of his personal identity and humanity.
When on the train a son beat his father to death, this shows an example of dehumanization in action. Starvation lead the people to dehumanizing each other even if that meant hurting family.
A concept of dehumanization would be the fact of the most traumatic happenings happen during celebratory holidays.