This is the residence of Yin, Yang and Master Yo, and the former residence of Ti and Chai who left Master Yo to watch over it when Yo was still a cub. Throughout the series, the dojo has been (partially) destroyed many times. Especially the walls/windows. After defeating the Nightmaster is it completely destroyed and Yo makes Yin and Yang rebuild it, starting with the outhouse.
There are a few locations in and around the dojo that recurring throughout the series.
Yin and Yang's Room
Yin and Yang share a bedroom. They divided it in the middle. While Yin's half of the room is usually neat and tidy, Yang's side of the room is a mess, a fact that triggered a few arguments between the two. Yin's side of the room contains a purple bookshelf a pink bed with nightstand and some (mostly) pink decorations. Yang's side contains training equipment, a blue bed and nightstand and a lot of mess. There's a shared table in the middle of the room.
Master Yo's Room
Yo's bedroom is small and most of the space is taken up by the bed. It's hardly ever seen on the show but bears some significance as this is where the previous WooFoo masters told Yo about his responsibility of training new WooFoo Knights.
The living room is one of the most commonly shown places of the dojo. It's where Yo's recliner resides and thus where he can be found most of the time. It gets destroyed quite a lot (presumably more than most other parts of the building).
Master Yo's Bathroom
In Camp Magic Pants, Yo get the bath in this room.
The WooFoo armory contains all of WooFoo's historical and important weapons (like the double-bladed blade of destiny, the adult diaper of doom, etc.). Villains often try to get access to the armory or at least some kind of artifact that is kept in there. The CPK want to raid the whole armory as soon as they hear about it, etc. A lot of the weapons are no match for Master Yo's WooFoo as seen when he becomes evil and Yin and Yang are forced to use the weapons against him. Over the course of the show some artifacts are added like the Lick-n-Stick.
In Brain Drain, Yang was teached by Master Yo to thinking but Yang was unable, but in the end of episode he handled it and he defeated Mastermind with it. In Imperfect Fooplicates, Yo gave Yin The Mystical Woo Foo Charm Bracelet's Fooplication Charm and she used it to make her and her brother's copies.
Vault of Secrets
There are some of historic artifacts where are not in Armory like Woo Foo Book of Forbidden Evil and The Woo Foo Spiral of Mystic Energy. In Brother Herman steals the Book of Forbidden Evil and in Attack of the Lesson Yin Yang broke two jars with two spirits Eats2Much and Duzznt Exercise, but they did not do anything because of human's laziness so they offscreen returned in the jars.
Secret WooFoo Lab
Yin and Yang are technically not allowed in the secret WooFoo lab. Although it seems to contain all sorts of potions and devices, it doesn't appear often. In "Woo Foo Flu", Master Yo uses it to find a cure against the magic sneezes of Yin.
Secret Woo Foo Battle Cruiser Room
It is big purple room in the middle with Woo Foo Battle Ship. It is accessible across Woo Foo Armory.
In Slumber Party of Doooom, Yang used the Book of Forbidden Evil to turn Lina and other girls to zombies and he and Yin were chased to the all of dojo included the unknown room in the Yin and Yang's room.
Yin's and Yang's training area is outside the building and inside a wall surrounding it. Sometimes there's dummies or obstacle courses for training purposes. There is also the dreaded outhouse that more often than not contains a panda.
Taking over the Dojo
Some villains have tried taking over the dojo or at least tried to take it from the WooFoos. Ultimoose built a mall around it to take it from them and Carl tried to make a sitcom out of Yin and Yang's life to take the dojo from them as their landlord.
It appears that the dojo has a really strong security system. One within the WooFoo armory, that Yang accidentally set off and Yin and him battled as a consequence. The other surrounds the whole dojo like a forcefield and is strong enough to keep Brother Herman out (as long as him and Carl don't work together). They even have a canon to shoot a ball of panda hair at their intruders, presumably just for Brother Herman.