http://df.magmawiki.com/index.php/Fey_mood#Possessed
gives the translation of various desires as seen in the (q) option in the workshop (s)he takes, when item not found
note that sometimes you need to adjust your settings from the manager (he assigns bones ahead of time for example, so if you got a manager order for bone crafts, you may have to remove it, if your weird one is asking for it)
In general they dont ask for anything you cant produce with some effort. However, for example, the fact that you could make glass, doesnt mean you have the industry setup ready, or that you mined metal ore doesnt mean you got metal blocks any time soon
Note that the above is true and useful, but wasn't your issue. Your dwarf wanted a workshop you didn't have - that's why he stood around. The best way to figure out what they want is check their skill set. It will be one of those skills, but one that is "moodable" (see description above - no moods associated with mining, for example...). If a dwarf has no moodable skills, they'll take a craftsdwarf workshop, as I understand it.
This is the best and only reason for a bowyers workshop if you have metal, for example.