In order to add a favorites system on your site, you must download and installed the Favorites for WP Job Manager plugin.
Once installed and activated Listify will begin using the Favorites addon as a "favorites" system. You will see a heart icon on each listing when viewing archives and again on the single listing page.
Clicking the heart will allow you to add a note about why you want to favorite this, and add it to your list. You can view what items you or another user has favorited by visiting your public profile page.