The specification codes for printing the early payment discounts are E46 (discount percent), E47 (discount base), E48 (discount date), and E70 (discount amount = rate x base). Put the desired fields onto your invoice specification to get this information to print.
Note that the discount information comes from the terms assigned to the customer in AR, and it does appear on the Totals screen. Also, the discount base needs to be manually entered at this time.