1. Navigate to the document in question.
2. Hover over the icon between the check box and the sender field
This will show information about that document as shown with the screen shot below. If the file has been processed from multiple places, the document will have been de-duped and the multiple source locations will be listed.
1. Select the list of files
2. Export their metadata using the standard.csv metadata group.
3. View the "Locations" field to see a source path.