How do you replace steering wheel off of a T600 Kenworth?

Depending on the model year, there'll be something covering the center of the steering wheel... could be a round horn switch, could be a larger plastic covering which also functions as a horn switch... it varies quite a bit, as the T600 was in production from 1986 through 2007. Once you've got that removed, you remove the steering wheel nut. Don't remember what size socket you need off the top of my head.

From there, you take a steering wheel puller, run bolts through the small holes of the steering wheel and the puller (3/8" standard thread, IIRC), run the big bolt through the center of the puller and make sure it's lined up with the steering column, turn it clockwise, and it'll pull the steering wheel off.

If you don't have a puller, a deadblow hammer can often get the steering wheel off... don't buy the Snap-On one, though - not worth it - get the $11 one from Harbor Freight. Once that nut is removed, give some good strikes in an upwards motion to the bottom of the steering wheel.