Get WooCommerce product category list in functions.php

You need to use action to get categories. in init action you can get product categories.

add_action('init', 'my_product_cat');

function my_product_cat() {
   $woo_cat_args = array(
      'taxonomy'     => 'product_cat',
      'orderby'      => 'name',
      'hide_empty'   => 0,
   );
   $woo_categories = get_categories( $woo_cat_args );
   echo "<pre>";
   print_r($woo_categories);
   echo "</pre>";
}