How to display custom fields of taxonomy in field twig
You can use item.content['#options'].entity.field_job_title.value to get the value of the job_titlefield value, I don't know if this is the best way to do it.
So your code will be something like:

{% for item in items %}

  &lt;div class="member"&gt;
    &lt;div class="name-box"&gt;
      &lt;div class="name"&gt;
        {{ item.content }}&lt;/div&gt;
      &lt;div class="position"&gt;{{ item.content['#options'].entity.field_job_title.value }}&lt;/div&gt;
    &lt;/div&gt;
  &lt;/div&gt;

{% endfor %}