Easiest is easy- all the constant traveling that Johto sort of requires at least in the beginning is basically Joker's previous life ANYWAY. The second he realized that, oh, he's not actually dead, he basically got up and started walking. I'd even throw in that the whole deal with these weird fantastical creatures everyone has to deal with is pretty easy too since he's used to dealing with exotic animals and unusual individuals. Honestly, Pokemon's core idea (travel a lot, get all these beasties) is the thing Joker has gotten used to the quickest because it's something he's already used to doing!

In contrast, the hardest part has been the hundreds of new technology that he's had to adapt to. Joker's good at hiding it, but the first few months he felt a little strange using the Pokegear just because it's so beyond even the idea of a regular telephone that it was sorta unsettling. That's not even talking about how complicated but vital it sort of is to a guy from freakin' 1880s England. And then it just keeps going on and on and on with all this new stuff... He still finds a lot of it fuckin' cool as hell, but it also leaves him feeling lost a lot of the time. All of it is part of the reason his bond with his starter Angel is so strong, because he really relied on her for a long while to help him deal with all the new things he had to quickly adjust to. He's not entirely sure what he would have done if he'd been one of the folks to start off with a non-humanoid Pokemon.