In Control Panel » Member Management » Edit Profile
Only Real / Display Email are shown/editable/searchable . I don't know why Registration Email is not shown . Maybe because not all forums verify users by email , But I think for most forums , this is informative for the admin . I've waited for this feature since wwwthreads...

Currently , the only way to get the user's reg email is through the SQL command.
I hope this can be added in the upcoming 7.4
(At least display/searchable . Uneditable is reasonable)

English is not my native language. I try my best to express my thought precisely. I hope you understand what I mean. If any misunderstanding results from culture gaps, I apologize first.