您已经走上了正确的轨道，只需将元键和元值参数添加到查询中

$args = array(
    \'post_type\'      => \'interviews\', 
    \'posts_per_page\' => 6, 
    \'post_status\'    => \'publish\', 
    \'paged\'          => $paged
    \'meta_key\'       => \'speakers_0_speakers_relation\',
    \'meta_value\'     => \'76\'
);
$loop = new WP_Query($args);