So! Right! If you're investigating and you want to learn a world's skills, it sort of depends if they're things you can pick up just from being there or if they're things that you would need to be taught.

Anyway, stuff like this Jaunt's creative magic and the various strains of Doki-itis from the Doki-Doki no Gakuen Jaunt and magical hero transformations from our last Jaunt world are inherent to the world enough that anyone visiting that world, Infiltrator or Investigator, will be able to just pick it up by being there. In that case, all you need to do is show your character doing the thing somewhere in your threads when you turn in AC and you're good for a skill proof.

But then there's stuff that people can't just pick up by being around, because they're things that even the people in universe need to be taught. Stuff like color magic from the Dolorosa Jaunt or Siren Song from the Shoals Jaunts or elementalism from the Bando Jaunt. With those skills, you need to show your character learning it from one of the other player characters when you turn in your AC for your skill proof.

(Infiltrators have it easy in a way, because even for the second category they can handwave that they were taught in their backstory and they just have to demonstrate their character doing the thing like an investigator would for the first category.)