To list all categories from custom taxonomy:

<ul>
<?php wp_list_categories( 'taxonomy=taxonomynameinslugform' ); ?>
</ul>

If you want to show all the categories, even the ones that are empty add the parameter hide_empty=0, for eg. taxonomy name is topic

<ul>
<?php wp_list_categories( 'taxonomy=topic&hide_empty=0' ); ?>
</ul>
Advertisements