Is there a way to get SKU numbers to show on a purchase order?SKUs are likely more important to be on POs than on any other form!

When you set up the product service/item and if you put the sku # in the item name, you should be able to customize your invoice and/or purchase order template to show this column.  You may also put SKU in the description.   

If you are looking to have a box put like where the order numbers are, etc. you may create a custom box but it would require manual data entry, which is not recommended as it can cause mis key errors,

Sku number really should be linked to the product itself and invoice and/or purchase order customized to show this field.