frontend editing, show selected category
Something like the following should work. This assumes that your category field handle is 'jobCategory', and has a limit set to 1.

{% set categories = craft.categories.group('jobCategory') %}
{% set entryCategory = entry.jobCategory.first %}
&lt;label for="fields[jobCategory]"&gt;Job Category:&lt;/label&gt;
&lt;select id="jobCategory" name="fields[jobCategory]"&gt;
    {% for category in categories %}
        &lt;option value="{{ category.id }}" {% if category.title == entryCategory %}selected{% endif %}&gt;{{ category.title }}&lt;/option&gt;
    {% endfor %}
&lt;/select&gt;