In the latest version of Jupiter X you can add your favorite custom icons,
Open the Custom Icons tab in the options panel and click on Add Custom Icon button, after this give it a name and upload a custom icon zip file. You can get custom fonts package from various websites like Fontastic, Fontello or Icomoon
Once you choose the icon package you will see your icons as a preview:
Scroll down and click Create button, now your custom icons are ready to use.
Custom icons can be used anywhere in Elementor with the widgets that support icons, once you click on choose icon you will have your custom icons set in the Elementor Icon Library