The "best" way to do it is not.
The Jira database is not built for reporting, and the worst possible way to report on Jira is via the data.
If you insist on doing this, you are going to need to connect to the database with a driver in powerbi, and build and maintain a useful data dictionary (this will need to change every time you upgrade Jira or install or upgrade an add-on). NEVER connect to the production database either. Your queries are going to be slow, inefficient and load the database heavily, and hence should never be run while Jira is active, you will need to report off a replicated copy.
Instead, you should be using REST to question Jira. Or an add-on that understands the Jira database.
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