For enabling the WPL PRO favorites widget, you can do the following:

1- Go to WPL->Activity manager and find listing_links (Pshow Layout) activity and click on the "edit" icon:

2- Enable Favorites feature:

3- Go to Appearance->Widgets and assign a (WPL) Favorites widget to one of your theme sidebars. This widget shows user favorites:

Note: Guest users can use this feature. Favorites listings saves on a cookie on the visitor device so no registration is needed.