How to get the unique categories from a list
Maybe not the most elegant, but something like this should work:

{% set entries = craft.entries.section('faqs') %}
{% set usedCategoryIds = [] %}

{% for entry in entries %}
    {% for category in entry.faqCategory %}
        {% if category.id not in usedCategoryIds %}
            &lt;li&gt;&lt;a href="#{{ category.title }}" class="filter" data-filter=".{{ category.title }}"&gt;{{ category.title }}&lt;ins&gt;&amp;nbsp;&lt;/ins&gt;&lt;/a&gt;&lt;/li&gt;

            {% set usedCategoryIds = usedCategoryIds|merge([category.id]) %}
        {% endif %}
    {% endfor %}
{% endfor %}