This is a super short quick guide if you want to get the class Battle monk.

This class unlocks both its class abilities and the ability to use unarmed weapon tree.

Cheat way.
Look up the save game edit guide. Go to the skillset in the sav.dat Then place 9 inbetween the [ ]. There you got battle monk and unarmed available.

For those who want to experience the ingame route. You will need the following.
Persuade 8
party of 4 around 10 can handle all but 1 encounter.
Self level of 20+

So past here are some quest spoilers.
First head to the temple in the swamp. This is not an easy trek and if you arent in your teens as a group of 4 you will be map dodging the overworld encounters. which is completely doable. I wish there was a good map available but i just havent found one. Once you get there talk to the name monk Manulpa (or something close to that) to start the quest. Follow the quest until you are back at the temple and be sure to side with the monks as you near the end. Following here is some highlights you need to be ready for.

Party of 10 is for the snake kill part of the quest this has you fighting 4 snakes. 3 are lvl 14 and 1 is lvl 20. These snakes have alot o hp. The good thing is you can pull them 1 at a time and lead them to your merry band with a ranged attack. Might take a few tries to get lucky enough to not get a down during the fight and then heal up and go for the next.

After the snakes you will follow the quest till it takes you back to the temple. Once there you will eventually have to choose between helping the monks or helping the other person. From what i know siding with the monks gets you the battle monk class, siding with the other unlocks the yanguan sword stuff unless you started with it. To note i havent explored the vs monks route.

So you side with the monks this means its time for a 1v1 duel against a lvl 20 yuan sword user. bring them potions cause this person is fast and relentless. once you succeed in winning talk to a few people and get a set of armor and the class unlock book which takes about 1.5 to 2 ingame days to read through and unlock.

Personal thoughts.
I kinda despise that the game makes you go after the battle monk class, but lets you start as a yanguan sword user. To this end it makes the save game edit route a bit more palletable.