The steering knuckle probably isn't bad. Not sure they can even go bad. The issue more likely is one 3 things, or a combination of them:
1) Hub/Bearing - can make different sounds from a growl to a creak while the wheel is rotating, often more noise when under load from a hard corner. Lift the car and tip the wheel/tire 12-6 o'clock for any play in the hub - even if there is no play it could still possibly be going bad, but that would be a giveaway.
2) Strut/Bearing - this is really what handles most of the steering duty, along with the lower ball joint. You can usually hear a pop, pop, kind of binding sound while turning slow, if a strut bearing is going bad. Sometimes you can see the spring and strut moving erratically through the fender gap from outside the car.
Other sources of front end noise are subframe(cradle) insulators and control arm bushing. The control arms are not to expensive, and not really that bad to replace. The cradle bushings are a job.
'98 SC Riviera • 268k miles • 298 HP/370 TQ • 0-60: 5.79s • ET: 13.97 @ 99.28 • 4087 lb • 20.1 avg MPG • Nelson Ledges Lap: 1:30
3.4" pulley • AL104 plugs • 180º t-stat • FWI w/K&N • 1.9:1 rockers • OR pushrods • LS6 valve springs • SLP headers • ZZP fuel rails
KYB GR2 struts • MaxAir shocks • Addco sway bars • UMI bushings • GM STB • Enkei 18" EV5s w/ Dunlop DZ101s • F-body calipers
EBC bluestuff/Hawk HP plus • SS lines • Brembo slotted discs • DHP tuned • Aeroforce • Hidden Hitch
'05 GTO • 49k miles • 0-60: 4.8s • 16.9 avg MPG • Nelson Ledges Lap: 1:26