There are two options for this:
1. If Automatic Registration is disabled, you can enable the 'Social Profiles - EasySocial' plugin. Then in the JFBConnect backend > Profiles section, there are options to display required fields/etc during the social registration. However, if Automatic Registration is enabled, the user will be created without any input on the front-end - therefore, if some of the social fields are not imported, the user can still be created.
2. If you'd rather go through the EasySocial registration flow instead of JFBConnect's mini-registration view, you can change the JFBConnect backend > Configuration > General > 'Registration Component' setting to EasySocial. Then when a user logs in with a social network, the profile data will be populated in the EasySocial registration fields.
-Melissa