Once you've logged in to the Mondelez Merch Store https://www.mondelezdsdstore.com, you can view your purple points by clicking Rewards Shop (Purple Points) located in the top navigation; shown to the right.
You will be automatically redirected to the Rewards Shop and logged in.
Your Purple Points balance will be at the top right corner of the store. If you do not see a balance then you do not have any points to spend.