vc_teaser_grid_title
vc_teaser_grid_thumbnail
vc_teaser_grid_carousel_arrows

   it's called in vc_teaser_grid shortcode for titles (headings)
   2 params are passed to this filter.
   $original - markup generated by visual composer for heading
   $params - array() with available variables.

Usage example: Place this php code in themes functions.php file

<?php 
add_filter( 'vc_teaser_grid_title', 'name_of_function_to_fire', 10, 2);
function name_of_function_to_fire( $original, $params = array() ) {
	// to see what all available params perform var_dump($params);	
	$output = '<h2 class="your-super-class">'.$params['title'].'</h2>';
	//
	return $output; // this will be used instead of the original markup
}
?>