You could do netstat | grep <port> .

If you set the type field to NodePort, the Kubernetes control plane will allocate a port from a range specified by --service-node-port-range flag (default: 30000-32767). Each node will proxy that port each (the same port number on every Node) into your Service.

You could get all services, grep node port and see what comes out.

$ kubectl get services --all-namespaces -o yaml |grep "nodePort:"|sort
  nodePort: 30215
  nodePort: 30274
  nodePort: 30312
  nodePort: 30342
  nodePort: 30344
  nodePort: 30386
  nodePort: 30517
  nodePort: 30738
  nodePort: 30863
  nodePort: 31063
  nodePort: 31162
  nodePort: 31445

Or pipe to jq with json output if you want a more elaborate listing with service names and so on.

Edit: the port range for node ports is normally 30000-32767 and should be reserved for Kubernetes use to avoid conflicts.

You can get all the services using

kubectl get svc --all-namespaces

Then you can grep using the type.

There you can see all the assigned ports. It's basic piping and output filtering.

kubectl get svc --all-namespaces | grep ClusterIP | while read -r _ _ _ _ _ port _; do echo "$port" ; done

Right approach is to let Kubernetes choose the nodePort automatically from the default allocated range(30000–32767). Don't include nodePort in your yaml.