How to parse RADIUS (Windows NPS) log via Prometheus?

Please tell me how to parse logs through Prometheus?

Example as How to visualize RADIUS connections

As you mentioned logs you need to convert them into metrics to be able to use Prometheus. There are various tools available to parse logs & produce metrics, including things like mtail & fluentd. You would run such an application continuously scanning for new logs configured to produce gauges, counters, etc. from the data obtained. This is then scraped by Prometheus allowing you to visualise it as you see fit.