Each trait has a difference source how to obtain it. Just go to a jewelry crafting table. Switch to the analyze tab. And then just hover over the missing trait and you get the information how to obtain jewelry with this trait.
But the 2 quickest ways and least frustrating ways are:
1. Ask someone if he could craft a learning jewelry with that trait (you will have to provide mats or gold because some are expensive).
2. Buy it from a guild trader.
guild vendors I have found work best