We are using 2013 SP1. When a component is saved using [Save & Comment], it allows to enter the comment. But the comment is not displayed anywhere in UI. If I use UserComment property available in the Component object, the value is always empty. How can I retrieve the comment?
I assume you are talking about the "Save & Comment" PowerTool?
In that case, the comments should be visible on the "Change History" tab that is also added by the same extension.
The data itself is stored in Application Data on the item with the Application ID 'ext:ItemCommenting'.
The PowerTools are open source and available on GitHub, so you can check out the code there if you want: