Reflective simply means to consider what you have read and record your feelings about the topic.
For example, recall the scene in "Night" where the Wiesel's family is being carted off in the trains to Auschwitz. How did it make you feel when Madame Schater is freaking out and screaming about the fires? How did you feel when the other people in the railcar act the way they do toward her?
Try also to analyze why you may have felt one way at first, but now feel differently. What I mean is, as you finish your reflection on each entry, you may want to see if your thoughts about the previous reflection are the same or have changed. Reflection is not about right and wrong, but connecting a reader and author.