// Portfolio CPT
function portfolio_cpt() {
  $labels = array(
    'name'               => _x( 'Potfolio Items', 'post type general name' ),
    'singular_name'      => _x( 'Portfolio item', 'post type singular name' ),
    'menu_name'          => 'Portfolio Items'
  );
  $args = array(
    'labels'        => $labels,
    'description'   => 'Portfolio items',
    'public'        => true,
    'menu_position' => 5,
    'supports'      => array( 'title', 'editor', 'thumbnail', 'excerpt', 'comments' ),
    'has_archive'   => true,
  );
  register_post_type( 'portfolio', $args );
}
add_action( 'init', 'portfolio_cpt' );

function portfolio_tax() {
  $labels = array(
    'name'              => _x( 'Portfolio Categories', 'taxonomy general name' ),
    'singular_name'     => _x( 'Portfolio Category', 'taxonomy singular name' ),
    'menu_name'         => __( 'Portfolio Categories' ),
  );
  $args = array(
    'labels' => $labels,
    'hierarchical' => true,
  );
  register_taxonomy( 'portfolio_category', 'portfolio', $args );
}
add_action( 'init', 'portfolio_tax', 0 );

<?php

$taxonomy = 'portfolio_category';
$terms = get_terms($taxonomy);

if ( $terms && !is_wp_error( $terms ) ) :
?>
    <ul>
        <?php foreach ( $terms as $term ) { ?>
            <li><a href="<?php echo get_term_link($term->slug, $taxonomy); ?>"><?php echo $term->name; ?></a></li>
        <?php } ?>
    </ul>
<?php endif;?>