OK, you have the T299SR. A very nice camper. It has been a number of years since I was in that model, but this should help.
In the bathroom, look around for an access panel at the base of the shower. It should be about 6" X 6" or so. It most likely will need a no. 2 square bit to take the 4 screws out.
You should see the shower pipe trap through that space and see some of the water pipes. There would be a blue one for cold and a red one for hot water, hoping you can see something in that area.
With the floor plan, the shower hot and cold should head towards the sink. Under the sink cabinet you should see the red and blue pipes again. They should connect between the 2 areas.
With the kitchen sink being on the opposite side of the camper, and "I think" your fresh tank water fill door on the right side (door side), I'm assuming the water pump is under the kitchen sink? Is that correct?
The issue may be, the broken line may be between the kitchen sink area and the shower area. Those pipes "might" go under the floor to connect the 2 areas.
Look at the pipes under the sink and then under the shower and see if that is how they get across the camper? under the floor.
If the broken pipe is above the floor, under the shower basin, see if if you can see it there.
If water is leaking out "under" the camper, then let's confirm that and try to get some pics of area of the water is coming out. Hopefully the leak is in an open area of black waterproof membrane and not above a gray tank or black tank.
We can help guide you on how to take the bottom apart, but we need to know more about the leak and where it "might" be before we start into the underside of the camper.
Hope this helps
John