WordPress comes with a widget that allows you to display recent comments from users in the sidebar. This option is very flexible since it doesn’t require you to install any external plugin.
How to Add the Recent Comments Widget
In order to add the recent comments widget go to Appearance->Widgets.
Now drag and drop the Recent Comments widget into the sidebar area.
Five comments are displayed by default but you can choose to customize it.
Click the Save button when you are done. Recently posted comments should now appear in your sidebar.