Photoshop CS6 has 3D when you have an Extended licence or a Creative Cloud subscription. The 3D menu does not appear when you have a Standard licence. Does that explain your 3D menu being missing?
Check the Tech Specs on the product page. If 3D doesn't show up, your system doesn't meet the requirements.
If you don't have a license for Photoshop Extended, then there will be no 3D menu.
If you have an extended license and your system does not meet the requirements, then the 3D menu would be disabled (grayed out).