As of Drupal 7.33, Drupal core has a theme debug mode that can be enabled and disabled via the theme_debug variable. Theme debug mode can be used to see possible template suggestions and the locations of template files right in your HTML markup (as HTML comments). To enable it, add this line to your settings.php:
$conf['theme_debug'] = TRUE;
You can enable it with drush using:
drush vset theme_debug 1
And disable using
drush vset theme_debug 0
