With the recent changes to Guild Wars 2 the process to acquire traits changed from a model of buying skill books at certain levels to gathering the traits from the world via various means. The traits are available still from a vendor but they cost gold and skill points; both of which are sparse for the average player in Guild Wars 2. Fortunately a reddit poster has put together an excellent guide for the traits broken down by zone and level.
The text is inserted after the jump: