You can change the "Leave a Reply" heading on the WordPress comment form by using the comment_form_defaults filter. Here's a snippet you can add to your theme's functions.php file or a custom plugin:
add_filter( 'comment_form_defaults', 'custom_comment_form_heading' );
function custom_comment_form_heading( $defaults ) {
$defaults['title_reply'] = 'Ask your question here';
return $defaults;
}
This will replace the default "Leave a Reply" with "Ask your question here" on all comment forms across your site.