RE: Track retail discounts
A view or report is not available OOB to track commerce discounts. You will need build a custom report to build. If you already have the transactions exposed into a BYOD/Azure data lake storage. You can use the following entities to create the report.
If you want to have quick look and create a report. You can view at the table from table browser. Please make sure that you apply kinds of filters like the transaction status, type from header table.
URL Ref:
https://xxxxx.sandbox.operations.dynamics.com/?mi=SysTableBrowser&TableName=RetailTransactionDiscountTrans&cmp=USRT&limitednav=true&lng=en-us