Power BI Desktop gets updated each month, packed with new functionality. When you encounter an issue and request help through the forums or with a colleague, one of the first questions you will be asked is "What version of Power BI Desktop are you running?"
You can easily answer this by clicking on File -> Options and Settings -> Options in the toolbar.
The Options dialog box will open and you can select Diagnostics to display the version. In the image below, I'm running the October release (version 2.40.4554.463),
Sam Lester (MSFT)