(Copied from: https://powerbi.microsoft.com/en-us/blog/announcing-report-commenting-for-power-bi-service-and-mobile/)
Back in September of last year, Microsoft announced dashboard commenting in Power BI. Since then, we’ve seen thousands of you leverage this feature to collaborate with colleagues and start discussions within your organization.
Today, I’m excited to announce that we are bringing the same commenting capability to Power BI reports! With report commenting, you can directly add comments to report pages or specific visuals to discuss your data. The best part is that when you start a new conversation, Power BI will do all the hard work to automatically bookmark your report view, so others reading the comment can see the report exactly as you did when writing the comment, complete with your original filters. Report commenting is also tightly integrated with mobile, making it easy for you to keep up with your conversations on the go. When you @mention others in your comment, Power BI will immediately send a push notification to their mobile device to grab their attention.
Sound exciting? Continue reading the rest of the blog to learn more about this feature. Or, head on over to your favorite report in the service or mobile to try it out for yourself!
Have a look here for more information: