Quest - not in db - click on ?

[Mossclaw]

This quest: Do the world a favor http://www.wowhead.com/quest=27187

did not display the ? mark to complete it. The error was not in db.

unloading Carbonite allowed me to click the ? mark and hand it in.

T.I.A. for all you do!

[Vampiebat]

I had the same.
To show the "?", simply open your quest log (L), and click on the yellow circle at the front of the quest name to hide it from your screen, and then click on it again to make it reappear.
And there you go, "?" has appeared!

[Turgis]

If the above does not work (or an even easier method) just hit Alt-L and it will bring up the blizzard quest UI where you can complete it.

[Jigain]

Or for an even easier method, disable Carbonite's function to move tracked achievements into the Quest Watch window. This stops Carbonite from suppressing the Objectives window, which is where Blizzard shows the "Click to complete" box.