
Spoilers!!!!!
He will go inside the dungeon with the Knights Guild. There are undead monsters and twin head ogres inside but initially it wasn't anything the Knights can't take care of. But then as you saw in the last page where the orc killed a kid in a school that is Jin Ah's school actually. The orcs will begin their killing spree and they'll be able to corner a few students including Jin Ah since monsters can feel magical energy from her (because of the High Orc shadows) they'll target her then the 3 high orcs will come out to protect her. At first it was okay since they are way more powerful than regular orcs but then the chief of the orcs will come and tear then repeatedly. First time Jin Woo felt that his sister was in danger he immediately headed back outside and decided to ride Kaisel to go to his sister since he just used shadow exchange to get to Busan. He left the ants and Beru to protect the hunters from Knight guild. Going back to Jin Ah so the high Orcs were repeatedly torn by the chief and as soon as he got close to Jin Ah, he grabbed her by the neck since he though that it was her controlling the immortal shadows, thankfully Jin Woo came slamming towards the wall of the classroom leaving a huge hole. The monsters all felt his scary ass presence. Then he went directly to hug his sister and check her she's okay but really scared he instructed his shadows to guard each of the remaining students outside since he doesn't want his sister to see what he'll do to the monsters. He's very very pissed because this low class monster yried hurting his sister. He basically massacred those bastards. Then the reps from the hubter association came but it's already finished so yeah.
Going back to the dungeon the ants were killing the monsters and eating their remains then they're almost near the boss's cave then the undeads came back to life Yeo Rim? (I don't remember her name) used holy magic once they're inside the cave to block the undead then they saw the boss which is a high class monster got beaten by Beru in 1 shot.

You can read the light novel if you really can't wait. Just go back a few chapters since this part is already at when they are inside the dungeon
https://www.readlightnovel.org/solo-leveling/chapter-140
Can someone spoil me with the next chapter. I love spoiler. Does Jinwoo got stronger more or is there any reawakened? Or is their enemy stronger than him?