Exporting contacts via J2XML is a very easy operation. You can export contact with J2XML 3.7 or above.
Log into your Joomla! 3.x administrator area
Install J2XML 3.7
Enable the plugin J2XML Export/Send buttons.
In the top menu, hover over Components and click Contacts >> Contacts
Check the checkboxes to select the contacts you want to export.
Click the export button.
If you are using J2XML 3.3 you cannot export contacts directly. You can export users and linked contacts
To export unlinked contacts you can use a workaround
Create a fake user.
Link all unlinked contacts to its.
Export the fake user.