Moonfinger

Buy Noctilucous Jade: First things first, you need to grab some Noctilucous Jade for your preparations. Head to the southern part of Liyue Harbor, near the Alchemy station. You'll find an NPC named Shitou there. Chat with him and make the purchase to get your samples.

Find the Giant Cooking Pot: Paimon's got a hunch, and it leads us to Mondstadt! Specifically, you'll want to make your way to Dadaupa Gorge, located to the east. The closest Waypoint is the one at Galesong Hill to the south. From there, head north until you reach a Hilichurl Camp. As you approach, you'll see a giant cooking pot. Deal with any basic Hilichurls hanging around it and then make your way over to the pot itself.

Heat the Pot with Pyro: Paimon's right, we need to get this pot nice and hot! If you don't have a Pyro character in your party, now's the time to add one. Characters like Diluc, Klee, or Xiangling are great choices, and if all else fails, Amber is always a reliable option. Use any of their Elemental Skills to gradually heat the pot, or go all out with an Elemental Burst to heat it up quickly. Be warned, heating it up will trigger another battle!

Defeat the Hilichurls: Get ready for another fight! This time, you'll face mainly Samachurls, including the Geo variant that likes to summon pillars to attack you from. If you have a ranged character, they can be super helpful here. Otherwise, use your Traveler's skills to knock them down and then unleash a barrage of attacks.

Heat the Pot Again: Head back to the pot with your Pyro character and start heating it up again using Elemental Skills. Once your heat gauge is almost full, brace yourself – another group of Hilichurls will attack! This time, a Mitachurl will join the fray, and it's a bit tougher. Make sure to focus on taking down the Mitachurl first before dealing with the remaining enemies, like the Dendro Samachurl.

Finish Heating and Trigger Scene: With the enemies dealt with, return to the pot one last time. Use your Pyro character to finish heating it up. This will trigger a cutscene.

Return to Liyue Harbor: Now that your task is complete, head back to Liyue Harbor. Find Shitou at the Jade Mystery shop again and let him know you've successfully purchased the third Noctilucous Jade.

Place the Noctilucous Jade: Your final step is to return to where you first saw Rex Lapis when you entered Liyue Harbor. Go to the highest point there. You'll see a glowing marker; head over to it and place the Jade to officially end this quest.