You probably can't find it in Part Design because, by default, it's not turned on.

What you need to do is switch to the Part Design workbench, and then use View + Toolbars and turn on (check) the REFERENCE ELEMENTS (EXTENDED) toolbar. That will give you the basic wireframe tools (Point/Line/Plane) while you're working with solids.

The toolbar might be hidden - I typically customize my toolbar to have 2 columns of icons in order to have everything I use available!