How to display the parent category on an entry page?
Assuming your categories are accessible from a Categories field called 'productCategory', and you only have 1 category assigned to each product, you can display the name of the parent category with:

{{ entry.productCategory.one() }}


Or you can loop through multiple Categories with:

{% for category in entry.productCategory.all() %}
    {{ category.title }}
{% endfor %}




And to get the category link for your breadcrumb, you could use something like:

{{ entry.productCategory.one().slug }}