What chapter is it in "Night," when the people on Eliezer's train trade their valuables for information for where they are going?

I think that you probably want to reread the second
section of the narrative.  This would have marked the only time in the book where the
Jewish people are on trains and possess valuables.  After this point, they go to
Auschwitz and the subsequent journeys are on foot and by train.  Yet, that particular
train journey does not contain individuals who have much in way of possessions.  It
would be in this second section where the Jewish people actually have valuables that
could be traded for value.  Additionally, I think it would mark the only other time in
the narrative where the Jewish people actually wondered where they were headed.  Sadly
enough, after this section, the tone of what is presented is one where many are resigned
to their fate of death or intense suffering.  There is a struggle for survival that
overtakes the desire to wonder as to what will be present in the
future.