My Jenkins is deployed on a Kubernetes cluster. I installed and tinkered with a few docker plugins but it still tells me docker wasn't found.
First of all, please read How do I ask a good question? on StackOverflow.
As your question does not contain many details It might be hard to find solution.
To proper working of Kubernetes Cluster, you have to install docker. Best way is to follow official documentation. For example, for Ubuntu check this tutorial. On the left menu bar you can change Linux distros, for MacOS or Windows.
Please keep in mind that each Kubernetes version is supported by specific docker version. You can check it here. Current K8s version is supported by docker versions: 1.13.1, 17.03, 17.06, 17.09, 18.06, 18.09.
If you will still have issue with docker, please update your question with more information (Versions, Env, Cloud/Baremetal) and error you are receiving.