Location: Gusu City
Petitioner: Wei Cunxu
Reward: Ghost Claws, Martial Arts Thoughts, 2,000 coins
The only real blockade to triggering this side quest is finding it in the first place. The petitioner, Wei Cunxu, is in Gusu City, a prominent location to the southeast of Wudang Sect. The tricky part here is that Wei Cunxu is inside the Gusu Martial Club, a sort of back-alley location that's easy to ignore as you walk down the city's main street. You'll find the club between Zhao Lun the Sea Merchant's store and the little square with the tailor and blacksmith.
Cunxu, the owner of the club, requires assistance. Apparently one of his brightest and most promising students, Wang Shitou, has absconded with a number of their instructional manuals. Cunxu needs them back. Fortunately for him, Yi recognizes the description of Shitou as someone he saw in Luo Village.
Leave Gusu City and trek back northwest to Luo Village. Wang Chen, the waiter out front of the inn, will tell Yi that Shitou has already left the village. He'll point you to Jinli Village, which you'll find by traveling west to Wudang Sect, then following the southeastern road until you see a waterfall. Go south past the waterfall and Jinli will be on your left.
Wang Shitou is standing north of the entrance and on your right. Speak to him and he'll quickly realize that the group is here to bring him to justice. A fight breaks though, though Shitou only uses relatively basic fist-fighting attacks, and you can bring your whole party against him. Pretty easy battle, so long as you have even one other party member.
Shitou flees after the battle, leaving behind the Stolen Manuals. Take them back to Gusu City (southeast / east of Jinli) and return them to Wei Cunxu to receive your reward.