Since these rules are generated by kube-proxy, I doubt it will write output to a log file. In general, iptables logs are generated by kernel, so depends on your OS, it can be found in /var/log/kern.log or messages.

You can use "kubectl logs <kube-proxy-pod-name> -n <namespace> --all-containers" to check the logs from kube-proxy pod, or "kubectl get events" to check k8s events.