Things we would want to learn about that could be brought through a self-directed learning approach would be scuba-diving.

Preliminaries to self teaching scuba-diving:

First we'd want to learn history and equipment naming.
Look at dangers and pitfalls with training.
Prerequisites needed before we'd start.

We could work toward showing our progress through a report, which is conventional. If the learning produces a tangible product, why not have the student present a completed product to the class?
Presentations, brochures, a discussion. A teacher can assess application of the learning rather than proof of learning.