How much dose a driver with a class b with air brake endorsement earn?

As much as their company is willing to pay them. You could have a Class B CDL and drive a trash truck, dump truck, roll off truck, oilfield truck, or have a job where driving isn't even the primary line of work. By the way, there is no such thing as an air brake endorsement on a US license - only a restriction for CDL drivers if they don't pass the written air brakes test and perform their pretrip and road tests in a vehicle equipped with air brakes.