I just discovered another way to get the SKU to print on the Purchase Order. This was suggested to me by the Quickbooks Online team member response, however, it was definitely not clear. This program is NOT user friendly and you must be willing to try different things until you find what works. Anyway, it was suggested that the SKU be input into the Description Field of the product of service that you are creating or already have created. What was not made clear was the Description Field that they were talking about. It is the Description Field under "Purchasing Information" which is found when you scroll to the bottom of the Product/Service Information Form. I simply copy and paste the SKU and then the Description into that field and it is now populating on the Purchase Order and is visible on the printed copy. Quickbooks online really should do a better job explaining how this works. Hopefully this helps others having difficulty.