In your template file for the single product (possibly single-product.php) you can use get_field() to get your field data.
<?php echo get_field( 'discount' ); ?>
If on another page you’ll also need to pass in the post ID. So if you’re on the homepage you’ll need to pass the product ID that you’d like to get the value for:
<?php echo get_field( 'discount', $product_id ); ?>
