Output a custom registration list on the single event page. Lists the answer to a custom question for each registration.

ee_custom_reg_list.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

add_action( 'AHEE_event_details_after_the_content', 'ee_custom_reg_list' ); // use a different hook point to change where this is displayed
function ee_custom_reg_list( $post ){
    global $wpdb;
    
    if( is_single() ){ // pass the $post->ID if you want to restrict this to a specific event

        $sql = "SELECT ANS_value ";
        $sql .= "FROM {$wpdb->prefix}esp_answer ";
        $sql .= "INNER JOIN {$wpdb->prefix}esp_registration ";
        $sql .= "ON {$wpdb->prefix}esp_answer.REG_ID = {$wpdb->prefix}esp_registration.REG_ID ";
        $sql .= "WHERE {$wpdb->prefix}esp_registration.EVT_ID = %d ";
        $sql .= "AND {$wpdb->prefix}esp_answer.QST_ID = %d";
        
        $registrations = $wpdb->get_results( $wpdb->prepare( $sql, $post->ID, 12 ) ); // 12 is the Question ID
        if ( $registrations ) :
        echo '<h4>Attending this event:</h4>';
        echo '<ul class="attendee-list">';
        foreach( $registrations as $registration ){
            $name = $registration->ANS_value;
            $html = '<li>'. $name .'</li>';
            echo $html;
        } 
        echo '</ul>';
        endif;
    }
}