In Product using liquid you only have access to the Product. If you want to access a specific Product Variant you have to loop through the Product Variants. Within the loop you have access to the metafields for a variant.
{% for variant in product.variants %}
// to display the variant metafields use {{resource.metafields.namespace.key}}
{{ variant.metafields.ShippingWeight.shipping_weight }}
{% endfor %}