As Shan has said above about the login email field, you can find the appropriate field in the Wix Members collection here.
https://support.wix.com/en/article/corvid-wix-members-privatemembersdata-collection-fields
Login Email (loginEmail)
https://support.wix.com/en/article/corvid-wix-members-privatemembersdata-collection-fields#login-email-loginemail480
Also, note that there was an issue with the Wix Members collection in Dec 2019, so you might have been affected by this, for more info you can simply search the forum for previous posts about this.