Go to Explore Invoices.  Filter on Tran Type <is equal to> CM, and add other other filter criteria like date, etc.  Click on Refresh.  Highlight a row in the Invoices grid.  In the Preview window, click on Invoice Applications, and it will list the invoices against which the credit memo was applied.  That's it.  You could also go in the opposite direction - filter on tran type = IN, etc - if there were any credit memo or cash applications, it will show them in the Invoice Applications preview grid.