mage-eventpress/inc/template-prts/thumbnail.php

<?php
if (!defined('ABSPATH')) {
    die;
} // Cannot access pages directly.

add_action('mep_event_thumbnail', 'mep_thumbnail');
if (!function_exists('mep_thumbnail')) {
    function mep_thumbnail()
    {
        global $post, $event_id;        
        ob_start();
        require(mep_template_file_path('single/thumbnail.php'));
        $content = ob_get_clean();
        echo apply_filters('mage_event_single_thumbnail', $content, $post->ID);
    }
}