Hi,

By default, the subtitle is only displayed on a single post. In case you want to show it in all layouts, please install the CodeSnippet plugin, then create a new snippet with the following content:

add_filter( 'the_title', function ( $title, $id ) {
    $sub_title   = get_post_meta( $id, 'penci_post_sub_title', true );
    $html_return = '';
    if ( $sub_title ) {
        $html_return = '<h4 class="penci-psub-title">' . $sub_title . '</h4>';
    }
    return $title . $html_return;
} );

Regards,
PenciDesign.