Related Taxonomy Doesnt Show any Posts

I’m not sure what the rest of your code looks like, but you are mixing up your $query variable and you are not sending your $query to the new instance of WP_Query. Also, there is no need to send an array to the “terms” parameter if you are only using one term. Try this.

<?php
// Set the args
$args = array(
    'tax_query' => array(
        'relation' => 'AND',
        array (
            'taxonomy' => 'location',
            'field' => 'slug',
            'terms' => 'california',
        ),
        array(
            'taxonomy' => 'genre',
            'field' => 'slug',
            'terms' => 'comedy',
        )
    )
);

// Make a new instance of WP_Query
$query = new WP_Query();

// Make the query
$query->query($args);

// Test for posts
if($query->have_posts())
{
    // Loop through posts
    while($query->have_posts())
    {
        // Set up the post
        $query->the_post();
        global $post;
    }
}
?>