Using get_post_meta would be the correct way to get a post (products) custom meta key value. If your meta key is wcv_custom_product_mycred_reward then:
$meta_value = get_post_meta( $post_id, 'wcv_custom_product_mycred_reward', true); //true if not array, false if array
Since your meta key starts with wcv_custom you dont have to save it on the add/edit product form, Pro automatically detects it as a field and will save it.