For live training, I can not recommend Guru Labs[0] highly enough. They offer many courses, but specific to your question, lots of container related courses[1][2][3][4].
I learned a lot of the concepts just by typing search terms into YouTube. “TechWorld with Nana” is one channel that comes up a lot and has good, digestible explanations.
Hussein Nasser too, but he has less content directly about Docker/k8s and more about networking. It's excellent though.
[0] https://www.gurulabs.com/linux-training/courses/
[1] https://www.gurulabs.com/linux-training/courses/GL340/
[2] https://www.gurulabs.com/linux-training/courses/GL360/
[3] https://www.gurulabs.com/linux-training/courses/GL355/
[4] https://www.gurulabs.com/linux-training/courses/GL390/