How do you lube sticking brake cable on a T600 Kenworth?

Air brake systems don't work that way - the brakes in that T600 have very little in common with the brakes on your personal car.

There is no brake cable. That's an FMVSS-121 air brake system. The brake pedal is attached directly to the treadle valve, and the return is by air pressure (on some model years, there's a brake return spring to assist with this). Either you have a faulty brake return spring (if yours is a model year which has one), or else you have a faulty treadle valve. Fee free to email me at the address in my profile page and better describe the symptoms to me, and I can do more to troubleshoot the problem you're having.The cable that you're seeing which comes out of the hub and spindle assembly is not a brake cable - that goes to the wheel speed sensor for the ABS system.