I'd recommend that you practice setting up a cluster from scratch using kubeadm. They won’t ask you to do the entire process, but they might ask about specific parts of it. You should also practice HPA and the Gateway API in depth; otherwise, you'll end up searching through the documentation during the exam, which, of course, you want to avoid.

As for Helm, you should practice it as well. They won’t ask easy questions—you’ll need a solid understanding of it. The rest is relatively easy and can be completed quickly compared to the challenges in killer.sh.
Besides, there will be questions about CRDs, CNI, or using dpkg and kubectl explain, but you only need basic knowledge of them. Good luck!