Which hook should I use for this scenario regarding the registration process and account/profile update?

You would want to use the user_register and edit_user_profile_update actions. In this way you’ll take care of both scenarios. Be careful. Both of these fire after the user information has already made it to the database.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)