I've been away from the enchanting-disenchanting field for quite a while. With this said, do you need to train for disenchanting and if so, where in Stormwind? I honestly, don't recall on this matter.
I tried to disenchant a 306 item and said I was too low. I was at 450 in Wrath but it's been quite a while since I used my enchanter.
Higher skill in enchanting lets you disenchant higherlevel items.
And no, you dont need to "learn" disenchanting since its automatic when you pickup enchanting.
You need a certain Enchanting skill level to disenchant items of increasing item levels. If you can't disenchant something, skill up Enchanting until you can.
my loc can de anything upto level 82, any thing over and he cant do it due to item level/skill level restrictions which is fair enough (he's 450 ench and level 68)