Deployment yaml files for kubernetes system services are typically found in /etc/kubernetes/manifests.
The yaml files for addons like kubedns, kube proxy, tiller, etc can be found in /etc/kubernetes/addons.
The default kubedns loglevel is 2, are you can see from looking at the logs for a kubedns pod.
$ kubectl logs kube-dns-v20-597689868c-9l29r kubedns --namespace=kube-system