On July 13, 2021 I earned my CKA: Certified Kubernetes Administrator certification.
The curriculum assessed covers the following, with weighting of each topic
|25%||Cluster Architecture, Installation & Configuration|
|20%||Services & Networking|
You can find a copy of the CKACurriculum v1.21.
My main study material was the "Kubernetes Fundamentals (LFS258) which I do not recommend. It had a lot of misaligned information due to bits and pieces of the course material being updated, so the examples and some content didn't line up correctly or make sense.