What are some good Kubernetes training courses?
To understand kubernetes internal, it's good to have good understanding of containers, docker, etc.

Here, is the list of useful docker and kubernetes resources: 

1) Play with Docker Classroom https://training.play-with-docker.com/

2) Docker Interactive Tutorials https://www.katacoda.com/

3) Play with Docker (PWD) https://labs.play-with-docker.com/
    Play with Kubernetes(PWK) https://labs.play-with-k8s.com/

4) Introduction to Kubernetes course on edX also his company, CloudYuga is a certified Kubernetes service provider and training partner

5) Blog by Docker Captain, https://collabnix.com/
    Also, search kubenetes blogs on Medium which are very useful. 

6) Kubernetes The Hard Way github repo by Kelsey hightower updated with latest kubernetes 1.12.0 version.

Hope this helps.