what did the author and moshe talk about ?

I'm not sure whether you mean the very beginning of the book when they talk about the Kabbalah, and Moshe teaches Eliezer...... or whether you mean a bit later when he returns to Sighet after time away and warns the people to leave because the Germans and death are coming. Moshe tells Eliezer all about his time in Poland and the Gestapo's actions there. Everyone believes he's gone a bit crazy.