When you're starting off, you need to use an inspector, such as Firebug, Chrome/FireFox default ones.
Inspect that element:
View attachment 104105
You can see it has a class of nodeLastPost, search that via appearance:
View attachment 104106
Comes up with a few results... the red box are CSS templates, so that's not where you'd adjust HTML.
The green ones are where this is located.
View attachment 104107
node_category_level_2 isn't very common unless you have a category in a category showing on the forum node list.
So open: node_forum_level_2
You can edit this html:
Code:
<div class="nodeLastPost secondaryContent">
<xen:if is="{$forum.privateInfo}">
<span class="noMessages muted">({xen:phrase private})</span>
<xen:elseif is="{$forum.lastPost.date}" />
<span class="lastThreadTitle"><span>{xen:phrase latest}:</span> <a href="{xen:link posts, $forum.lastPost}" title="{$forum.lastPost.title}">{$forum.lastPost.title}</a></span>
<span class="lastThreadMeta">
<span class="lastThreadUser"><xen:if is="{xen:helper isIgnored, $forum.last_post_user_id}">{xen:phrase ignored_member}<xen:else /><xen:username user="$forum.lastPost" /></xen:if>,</span>
<xen:datetime time="$forum.lastPost.date" class="muted lastThreadDate" data-latest="{xen:phrase latest}: " />
</span>
<xen:else />
<span class="noMessages muted">({xen:phrase contains_no_messages})</span>
</xen:if>
</div>