Show categories List of Q&A Plugin

Hello i want to show Q&A categories List at website template page it showing nothing i am using this below code can someone please help me to find what i am doing wrong

<?php
//list terms in a given taxonomy using wp_list_categories (also useful as a widget if using a PHP Code plugin)

$taxonomy = 'question_category';
$orderby = 'name';
$show_count = 0; // 1 for yes, 0 for no
$pad_counts = 0; // 1 for yes, 0 for no
$hierarchical = 1; // 1 for yes, 0 for no
$title = '';

$args = array(
'taxonomy' => $taxonomy,
'orderby' => $orderby,
'show_count' => $show_count,
'pad_counts' => $pad_counts,
'hierarchical' => $hierarchical,
'title_li' => $title
);
?>

    <?php wp_list_categories( $args ); ?>