Nginx ingress controller not giving metrics for prometheus
I would follow this guide to setup monitoring for Nginx ingress controller. I believe what you are missing is a prometheus.yaml which defines scrape config for the Nginx ingress controller and RBAC for prometheus to be able to scrape the Nginx ingress controller metrics.
Edit: Annotate nginx ingress controller pods
kubectl annotate pods nginx-ingress-controller-pod prometheus.io/scrape=true -n ingress-nginx --overwritekubectl annotate pods nginx-ingress-controller-pod prometheus.io/port=10254 -n ingress-nginx --overwrite