Well your code doesn’t do anything right not to actually fetch the info. 🙂
You need to run it through a custom wp_query AND add the appropriate posts_where filter function as described in the documentation
Take a look at example 4 here: http://www.advancedcustomfields.com/resources/query-posts-custom-fields/
So your code needs to be more like:
<?php
//Get the volunteer posts ID
$post_id = get_the_ID();
//Fetching all shows the volunteer was actor in
$args = array(
'numberposts' => -1,
'post_type' => 'show',
'meta_query' => array(
array(
'key' => 'cast_%_actor',
'compare' => '=',
'value' => $post_id,
)
)
);
$show_actor_query = new WP_Query($args);
?>
<?php if( $show_actor_query->have_posts() ): ?>
<?php while( $show_actor_query->have_posts() ): $show_actor_query->the_post(); ?>
<h1><?php the_title(); ?></h1>
<?php endwhile; wp_reset_postdata(); ?>
<?php endif; ?>
I can’t really write all the code for you because it’d be a bit over the top and I strongly believe in learning by doing 🙂 But I’ll be happy to guide you in what you need to do.
Here you can read more about the WP_Query object
http://codex.wordpress.org/Class_Reference/WP_Query
