I need the code to a 2000 yukon abs brake light to turn off after changing the brakes

If your ABS light is on, changing the brake (pads) won't fix the light.
There are several reasons for the ABS light to go on, and probably the most common is the connection to one of the four wheel speed sensors, or bad sensors. On most GMs, the sensor and wheel bearing are one assembly.
First, you need to get the error code read via the OBD2 plug. The dealer can do it of course. And many parts stores, such as AutoZone will scan for codes for free.
The code will give you a clue to the problem. Until the problem is fixed, the light can be reset, but it will turn back on almost right away.