This should get you started
function my_cpt_cats() {
$parent = get_term_by( 'slug', get_query_var( 'term' ), get_query_var( 'taxonomy' ) );
$args = array(
'type' => 'post',
'child_of' => $parent->term_id,
'parent' => '',
'orderby' => 'slug',
'order' => 'DESC',
'hide_empty' => 1,
'hierarchical' => 1,
'exclude' => '',
'include' => '',
'number' => '',
'taxonomy' => 'YOUR_TAXONOMY',
'pad_counts' => false
);
$categories = get_categories( $args );
}
Remember to use your taxonomy name in the $args array.