From questden

This template cites a quest (or questarch) thread as a source. At the moment it doesn't do the whole Mediawiki references dance (those need an extension) and just tries to make a link to the post. It needs to know the thread number as well as the post number to do this.

Usage: {{citeq|thread=N|post=M}} where N is the first post of the thread.

You can also specify an optional board argument, e.g. board=questdis.