How to troubleshoot metrics-server on kubeadm?

Edit the metric-server deployment like Subramanian Manickam's answer said, you can also do it with

$ kubectl edit deploy -n kube-system metrics-server

That will open a text editor with the deployment yaml-file where you can make the following changes:

Under spec.template.spec.containers, on the same level as name: metrics-server add

args:
- --kubelet-insecure-tls
- --kubelet-preferred-address-types=InternalIP,ExternalIP,Hostname
- --metric-resolution=30s

and then under spec.template.spec at the same level as containers I also had to add:

hostNetwork: true

to fix the metrics-server working with the CNI (calico in my case).

Afterwards your deployment yaml should look something like this:

[...]
spec:
  [...]
  template:
    metadata:
      creationTimestamp: null
      labels:
        k8s-app: metrics-server
      name: metrics-server
    spec:
      containers:
      - args:
        - --kubelet-preferred-address-types=InternalIP,ExternalIP,Hostname
        - --kubelet-insecure-tls
        - --metric-resolution=30s
        image: k8s.gcr.io/metrics-server-amd64:v0.3.3
        imagePullPolicy: Always
        name: metrics-server
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
        volumeMounts:
        - mountPath: /tmp
          name: tmp-dir
      dnsPolicy: ClusterFirst
      hostNetwork: true
[...]

After that it took about 10-15s for kubectl top pods to return some data.

You have to add this command section after line number #33 on metrics-server-deployment.yaml file.

  command:
    - /metrics-server
    - --kubelet-preferred-address-types=InternalIP
    - --kubelet-insecure-tls

Once you have updated the file, you have to re-deploy the pod.