You can add scrape_interval parameter in your configuration by default it is every 1 minute scrape_interval: 5s
Prometheus has its own query language called promql. You can learn more about this language from this here https://prometheus.io/docs/prometheus/latest/querying/basics/
There are lot of metrics you can define for Kafka. I will mention a few of them in this article
Read on for a breakdown of some of these measures.