Modifying PO xml

I am trying to modify the po xml template so that my account number for the supplier shows up on the PO. I am willing to replace "Requisitioner" with "Account Number". I need to know what to put in place of the "|" PurchaseOrder.Requisitioner so that the value that I pull from the "Account Number" field on my supplier screen shows up in that field. Any help is greatly appreciated Thx Dave