What is fastest learning path for learning Power BI?

Recommendation to start here with these free courses

Ultimate Beginners Guide to Power BI

http://portal.enterprisedna.co/p/ultimate-beginners-guide-to-power-bi

Ultimate Beginner Guide to DAX

http://portal.enterprisedna.co/p/ultimate-beginners-guide-to-dax

Free Power BI resource downloads available here

https://enterprisedna.co/power-bi-resources

Then review some recent free training workshops from Enterprise DNA for some real-world application of Power BI (Few links below)

Discovering Advanced Insights w/Power BI - https://www.youtube.com/watch?v=XzgNUYz8_TI&t=308s

Effective Power BI Reporting - https://www.youtube.com/watch?v=HwawCW_3mI4

For advanced training check out all the courses and resources available at Enterprise DNA Online

http://portal.enterprisedna.co/

Also Enterprise DNA TV for Power BI topic deep dives - https://www.youtube.com/c/EnterpriseDNA