Where there is a will there is a way.

While I agree that Intuit should allow users to customize what "prints" on a Purchase Order form and don't agree that you can add the SKU field to a PO and yet it will not print on paper, you can always "right-click" and print to PDF while you are in the Purchase Order that "does" show the SKU number and then print that to paper if it is absolutely necessary to do so. I personally don't print things out on paper anymore, I PDF everything. And while it is not pretty, the snip-it of the PDF copy of the PO I created attached does include the SKU number.