He is not in the huge s- rank gate but rather he went in to another lower level gate that contained a double gate. Before entering the double gate he told everyone there to leave and tell the hunter association that he was there and that there was a double gate. This is also how the blond guy knew he was in there and why the brought a group of hunters to help out .
It's not the huge one in Japan, it's what appeared to be a high ranking one but in the end was actually a "double dungeon" (sorry if it's not the right name) and that was at least part of the reason they went to where he is. They knew where he was because the guild that was supposed to raid it informed them of his taking over the gate. The thing about looking for him for the other gate I'm not sure about, 'cause from what I remember the hunter association found out about how the Japanese guild wanted to off the other teams in the big raid to get all the credits and so were not exactly inclined to help them. Hope it helps ^-^
from what i understand, he's currently in a double gate? idk whats the name, and people know the double gate is a strong gate, thats why the blonde came and call other strong hunters. the blonde know jinwoo is there because someone called him before, and the gate jinwoo currently in is the gate from the school before (and he got the key to enter) so its not the s rank gate in japan
im sorry if its confusing, english is not my first language ⁄(⁄ ⁄·⁄ω⁄·⁄ ⁄)⁄
okay wait, just confirming, so is jinwoo currently in that huge s-rank gate that the guilds have been planning for...? or did those other hunters just know that he was currently doing a raid elsewhere and went to it because theyre looking for him? bc that one blonde dude knew that he was in there when he was talking about the power coming from it and what not