You might be interested in this post by u/sunagainstgold as well as the follow-ups by myself a couple posts down. u/itsalrightwithme has written before about the rise of mercenaries and the swiss specifically here and here.

The actual training undergone by mercenaries could vary widely depending on the company. The main advantage of the mercenary system was that a monarch wouldn't have to worry to much about the exact details of raising and supplying troops, instead passing that duty onto contractors who would presumably have some prior military experience and would know how to turn new recruits into effective soldiers.

Depending on their background, many recruits might have had some degree of martial training prior to joining. The Swiss militia system famously created a crop of men who were trained year round in both fighting and maneuvering as a group. Elsewhere, for example Germany, you might have common festivals in which civilians showed off their prowess various weapons for a chance to win prizes along with shooting contests to demonstrate skill with the bow, crossbow or handgun. In england it was expected that pretty much every yeoman had a familiarity with the use of the longbows and billhooks. In addition, members of lesser nobility in western europe might know how to use a variety of weapons from their upbringing.

Depending on the captain, weapons practice such as pike fencing or target practice with firearms might continue, however increasingly the most important training was becoming drill, discipline and maneuver. This was especially true for pikemen which needed to memorize commands, maintain a cohesive formation while moving and fight without crowding their neighbors in order to be most effective. Pike squares at the beginning of the 16th century tended to get pretty large, at times more than 50 ranks deep. When arranging troops for combat, the newest recruits tended to be placed farther back where they would be largely out of harms way while the best equipped and most experienced would be given pikes and put in the front ranks, where most of the fighting was expected to happen. As his military career went on a landsknecht might get the opportunity to literally move up the ranks and start earning better pay.