looking at the user_register action through gravity form and normal WP paths

user-registration-action.php

add_action( 'user_register', 'explore_user_stuff', 10, 1 );
 
function explore_user_stuff( $user_id ) {
   write_log($_POST);//will have info if done through typical WP fashion but not if through gform
   write_log($user_id);//has user ID no matter what
   $user = get_user_by('id', $user_id);//get user info
   write_log($user);
}


//LOGGER -- like frogger but more useful

if ( ! function_exists('write_log')) {
   function write_log ( $log )  {
      if ( is_array( $log ) || is_object( $log ) ) {
         error_log( print_r( $log, true ) );
      } else {
         error_log( $log );
      }
   }
}