The premise of my story is that we have discovered a parallel Earth (let's call it E2) lying next to ours (let's call this E1). Something has gone wrong on E2 - at some point in its past, it went through some sort of apocalyptic event that decimated most of the people living in it. The remaining survivors have broken up into roughly two factions - normal humans, and people that were impacted by the event, turning into some sort of demonic entity (they continue to maintain sentience/intelligence).
The second aspect of this story is that, in both worlds, there are certain individuals known as Wanderers. These Wanderers have the ability to traverse between E1 and E2. What's more - Wanderers from E2 (I'll call them Dark Wanderers) have been coming to E1 for many years, with the purpose of kidnapping humans to use for their own purposes - slave labor, breeding stock, fodder for their war against each other and the regular survivors on E2.
There is a clandestine government agency on E1, headed by a group of Wanderers whose mandate it is to travel into E2, and essentially wage a secret war against the Dark Wanderers. Their job is to conduct rescue missions on kidnapped humans from E1, and assist the regular survivors on E2 in their wars against the Dark Wanderers, destabilizing their settlements and operations, and if necessary, killing them when required.
Now, these Wanderers from E1 could be anyone - the ability shows up randomly in people, so the recruiting pool for potential candidates is very, very small to begin with. It could be an 80-year old grandma or a 5-year old kid in kindergarten. And on top of that, very few people would even want to take on a task this dangerous and terrifying.
So let's assume that, for the most part, any Wanderer trainee that decided to join the agency is completely new to any kind of military/special forces style operations. Let's also assume that the agency typically targets able-bodied adults ranging in age from their early 20s to 30s to ensure they're in their physical prime.
What kind of training would the agency need to provide these individuals to get them ready for their missions on E2? Off the top of my head, they would likely require firearms training, significant strength and cardio training, a fair bit of hand-to-hand combat, basic first-aid, navigation/wayfinding (electronics don't work too well on E2) and basic bushcraft. I would also have them do some guided practical missions with a mentor on the field so that they can get an idea of what they're up against. Maybe even the usage of a simulation of some kind?
What else could the agency teach these guys/girls? Also, what would the right duration of training be? Seems like for something like this, a minimum of a year is almost a must? Probably even more?