Which action does wp_update_user triggers?

wp_update_user() is in /wp-includes/user.php lines 1401-1439. It uses wp_insert_user() (same file, lines 1254-1380) to update the existing user or add a new one if the user doesn’t exist. That function is where the various filters and actions affecting user account info live, and shows everything you can do to the $user object.