How to get template link?

If you’re using that template for only one page, you can try this function:

/**
 * @param  string  $template  Base name of the template.
 */
function wpse_233924_get_page_link($template)
{
    $query = new \WP_Query;

    // Get page which is using the $template.
    $page = $query->query([
      'post_type'      => 'page',
      'meta_key'       => '_wp_page_template',
      'meta_value'     => $template,
      'no_found_rows'  => 1,
      'posts_per_page' => 1 // Retrieve only one result.
    ]);

    return isset($page[0]) ? esc_url( get_page_link($page[0]) ) : false;
}

Then:

$page_url = wpse_233924_get_page_link('template-portfolio.php') ? : '#';

?><a href="https://wordpress.stackexchange.com/questions/233924/<?= $page_url ?>">View portfolios</a><?php

Note that WordPress recognizes page-templates folder by default. So, if you put the template-porfolio.php inside that folder, the value of $template must be page-templates/template-portfolio.php.