Sample code
{% for line in line_items %}
{{ line.product.metafields.namespace.key }}
{% endfor %} Examples of Liquid drops to use in e.g. a Shopify notification template:
{{ order.metafields.c_f.purchase_order_reference }}
{{ order.customer.metafields.c_f.id }}
{% for line in line_items %}
{{ line.product.metafields.c_f.gift_option}}{{line.variant.metafields.c_f.washing_instructions }}
{% endfor %}This example only applies to Shopify's internal notification templates. If you want to use the Order Printer app, metafields will not be available, so another approach is needed - please see this article from Shopify
You may find more detail about line item at https://shopify.dev/docs/themes/liquid/reference/objects/line_item
