functions.php

<?php
global $wpdb;

$debug = $wpdb->get_col( $wpdb->prepare(
	"
	SELECT pm.meta_value FROM {$wpdb->postmeta} pm
	LEFT JOIN {$wpdb->posts} p ON p.ID = pm.post_id
	WHERE pm.meta_key = %s 
	AND p.post_type = %s
	",
	'_tribe_rsvp_full_name', // Meta Key
	'tribe_rsvp_attendees' // Post Type
) );

print_r( $debug );