Hi,

What you need to change?

In your case you need to remove the filter:

remove_filter( 'vc_gitem_template_attribute_post_title_with_date', 'thegem_attribute_post_title_with_date', 10, 2 );

And then add your one in the child theme...

Hi,

can't I overwrite additional.php file? -  no. it's not template.

 In what position can I insert it into the child theme?  - Sorry?

Code example:

remove_filter( 'vc_gitem_template_attribute_post_title_with_date', 'thegem_attribute_post_title_with_date', 10, 2 );
add_filter( 'vc_gitem_template_attribute_post_title_with_date', 'thegem_attribute_post_title_with_date_new', 10, 2 );
function thegem_attribute_post_title_with_date_new( $value, $data ) {
    extract( array_merge( array(
        'post' => null,
        'data' => ''
    ), $data ) );
    return '<div class="post-title"><h4 class="entry-title"><a href="'.esc_url(get_permalink()).'" rel="bookmark">'.mysql2date('d M', $post->post_date).': <span class="light">'. get_the_title($post->ID) .'</span></a></h4></div>';
}
add_shortcode( 'gem_post_title_with_date', 'thegem_post_title_with_date' )

You're welcome!