How can I display the cart diagram at the top of the TOP page?

Use your design.
Cart URL can be generated using osp-cart route.

I succeeded when I referred to the posts of other people.
Thank you! Everyone in the forum!

header.php



 <?php if(function_exists('osp_install')) { ?>
            <?php
              $cart_count = 0;
              if(osc_is_web_user_logged_in()) {
                $cart = ModelOSP::newInstance()->getCart(osc_logged_user_id());
                $cart_count = count(array_filter(explode('|', $cart)));
              }
            ?>


            <a class="cart tr1" title="<?php _e('Cart', 'alpha'); ?>" href="<?php echo osc_route_url('osp-cart'); ?>"><i class="fa fa-shopping-basket"></i> <span class="counter"><?php echo $cart_count; ?></span></a>
          <?php } ?>

@sezy2021
That is solution as well.