Impossible. Right click on any footage layer except a shape layer and select Reveal Layer Source in Project. If you have folders in the Project panel your pre-comps may be in one of the folders.
You can rename layers in the Timeline but changing the Layer Name does not change the Source Name. The timeline can display Source Name or Layer Name by simply clicking on the header.
The only layers that do not show up in the Project Panel are shape layers.
As always: Screenshots tell a lot. As Rick said, you can't see what doesn't exist in your project window - unless, of course, your pre-comps are buried inside one of your organizational folders in the project window.