Suggestions to improve knowledge on docker
Some good next topics for the real world are...


Security. There are several security concerns with docker, for example 


Is there a problem running stuff inside the container as root?
Is there a problem giving non-root users on the host access to the docker daemon?
Is there a problem with the docker daemon running as root on the host?
All three can be solved with docker out-of-the-box. Learn how to.

Networking. Check out the docker networking options.
Image sizes are a recurring problem, especially if you build your stuff inside a docker image. Your average naive first build image may be 1GB or more - try to get the same image, whatever it is, to 500, 300 or 200 MB.
Docker volumes; how to get configuration into your containers; etc.
Private artifact repositories.
Explore the environment: docker compose, docker swarm, etc.
Finally, take  a big leap on to your next technology... OpenShift? Kubernetes?