Your question is a bit vague at best.
Are you looking for community-written tests to help you see how much you've learned, or how much you have yet to learn?
The easiest way to learn, and to see what you have left to learn, is to set up a box yourself. Get a functional network, maybe some services (apache and ssh), and eventually upgrade a kernel. You will really be able to explore and grow in whatever directions you'd like, at your own pace.