Subtitles – need two variable names from Newspaper

I am starting to use “Nelio Content” to automatically move posts from our WordPress site (BCWorldview.org) to our Medium.com site. What is missing in the transfer is the Subtitle field in Newspaper. Nelio Content gave me the following PHP to make this work, but the variables noted below need to be replaced with the correct Newspaper function names. Can you provide those names so this code will work within the plugin “Snippets”? Thanks…

————–
add_filter( ‘the_nelio_content’, function ( $content, $post_id ) {
if ( ​has_subtitle( $post_id ) ) {
$content = get_the_subtitle( $post_id ) . $content;
}
if ( has_post_thumbnail( $post_id ) ) {
$content = get_the_post_thumbnail( $post_id ) . $content;
}
return $content;
}, 10, 2 );

Note that the functions has_subtitle and get_the_subtitle are functions that I made up. You should check on your theme if similar functions exist or what is the way to recover the subtitle value from the database.
—————-