2) Which reports you frequently used in jira?

We use agile under that we have :
Burndown chart: Tracks the total work remaining. It helps your team to manage its progress.
b) Sprint Report: Tracks the work completed or pushed back the backlog into each sprint. It helps you to determine if your team is not overcommitting.
c) Velocity Chart: tracks the total work completed from sprint to sprint. It helps you to determine your team’s velocity.