It's unclear when this term first came into use on The Land, though presumably not until at least the second century, and more likely a good deal later than that. Early in the world's history, it was common for all of the few people who existed at the time to perform whatever tasks were necessary for survival, as well as whatever was of interest to them, personally. Over time skills became more specialized, and particularly after the introduction of money in LY 107, individuals began taking on more specific jobs. However, there have throughout history always been those few people who, for whatever reason, never settled upon one particular job. It could be that they had difficulty deciding on one they liked, or else difficulty finding one for which they had sufficient aptitude. Others may have been good at any number of jobs, all of which they liked, and simply saw no reason to limit themselves.
It should also be said that it's unclear when the position of master first became common, though it was most likely around the same time as specialized jobs, possibly even prior to the introduction of money. The term "Jack of all trades" is actually a subphrase from Earth, which is sometimes rendered in a longer form "Jack of all trades, master of none." This phrase, of course, makes little sense on the Land, as even those people who learn only one trade rarely become actual masters. However, Jacks of all trades are well known for having many different masters. There is no set number of how many trades an individual must learn to deemed a Jack of all trades, nor what types of skills. In fact, many of the skills they learn may not be considered trades at all, not something they could use as a regular job. It is also at the discretion of each master to determine when their student has learned enough. With students who they know don't intend to learn a single trade, they will likely teach at an accelerated rate, yet still end up teaching far less than they would to a proper apprentice who is truly learning their trade as a presumably life-long career choice. In this light, it might be said that Jacks of all trades not only are masters of none, but also... well, an official term doesn't exist. One might say "graduates of none" or "adepts of none" or to borrow another Earth term, "journeymen of none." However, it is not uncommon for Jacks of all trades to have an innate capacity for learning more at a faster rate than the average student can handle, and it is therefore unfair to assume their skill level at any one trade is in any way lacking.
It should further be noted that, while it's entirely possible to meet and learn from different masters in any one village, it's far more common for Jacks of all trades to style themselves as adventurers, and wander between various villages, hoping to find both masters more highly skilled at a particular trade than those of other villages, and places that the trades they've already learned might be more profitably plied. However, it's also common for Jacks of all trades to have no particular plans for what to learn or how, when, or where to use whatever skills they acquire in their wandering. They may prefer simply to have a wide set of skills at their disposal to use whenever the need should arise.