Catalog > Attributes > Manage Attributes > [...search for sku...]This worked in Magento Community version 18.104.22.168
Scroll down to Frontend Properties > Visible on Product View Page on Front-end > Yes > Save
After that, you will want to refresh your cache to make sure things register properly on the frontend.
Thursday, June 18, 2015
How to show SKU on Magento Product Page
If you're looking to display SKU on the product page, it's easier than you think. Just follow the directions I found online.