Showing a list of selected/related categories to entry
Indigo Viking's code will achieve what you want, but if you want a simpler solution (possibly a bit more performant since there's no second for loop), you could do this instead:

{% set suitability = craft.categories.group('suitability').all() %}

{% for category in suitability %}
    &lt;dt class="data-list__item data-list__item--title"&gt;
        {{ category.title }}
    &lt;/dt&gt;
    &lt;dd class="data-list__item data-list__item--value"&gt;
        {% if category.id in product.suitability.ids() %}
            Yes
        {% else %}
            No
        {% endif %}
    &lt;/dd&gt;
{% endfor %}


The way this works is product.suitability.ids() returns an array of the element ids of the categories selected in your suitability field. Then you just check if the current category's id is in that array.

Fast, simple, and easy!