There is a dwarf that "has been possessed" and now he's in the meeting hall waiting for something. I'm guessing I don't have the workshop he needs but how can I found out?
Check his skills.
He's likely to want a workshop related to one of the skills he already has.
Note that precursor making skills like weaving and mining relate to the workshop to which the production skill is related; a weaver will want a Clothiers Workshop; a miner will want a Masons Workshop; and a tanner, if they mood at all, will want leather works.