Site Duplicate let's you duplicate entries across Sites in Craft CMS. It even works when section entries aren't set to propagate across site sections making it easy to duplicate entry data between Sites.
How It Works
The plugin enables you to add a sidebar widget to selected sections for which you would like to be able to duplicate entries across Sites. The widget will display available Sites for the current section. For more information and known limitations about duplicating entry data please see the Github documenation page.