I have a level 30 woodworker and I want to be a carpenter. I have a level 30 provisioner and I want to be a cook. I've traveled all over the place and can't seem to find the person who lets me choose a subclass.
If you're a woodworker and provisioner you've already passed through the craftsman sub class to get there. A provisoner IS a cook. If you want to change woodworker to carpenter you'll need to go back to your tradeskill trainer and switch class, which will knock you back to level 10 and you'll have to work through the sub-class again to choose carpenter. Personally I'd just level up another character.
Sounds like you already did if you are level 30, you pick your subclass at 10 and your for real class at 20. So if you are level 30 you chose wrong. But a provisioner is a cook we don't have a TS class called cook.
Here's the bit about tradeskill respeccing if you truly want that one to be a carpenter: http://eq2.eqtraders.com/articles/article_page.php?article=g147&menustr=040000000000