Recently purchased an 09 lnf cobalt, needed some TLC so I've slowly been working on it. Got to the front suspension and I'm unsure what the issue is.

The there is enough play that the "neutral position" of my steering wheel shifts from turn to turn. I replaced the ball joints thinking it was a simple fix however there was little to no change.

These are my current thoughts:
1) worn knuckle? Although I've been told it's not a wearable item
2) wrong suspension parts? I didn't realize initially that there were different types. The current ball joints are for the soft ride suspension (k80566). Looking at the previous owners repair receipts the control arms are also for the soft ride. Would changing these to the performance variants make a difference?
3) issue with the hub/wheel bearing? A couple shops I talked to said it could be if the ball joints are new. However, the is no vertical play in the wheel.

 

The hole in the knuckle for the ball joint stud on the LNF vehicles is larger than all the rest. Very possible your issue is that, especially if using the soft ride parts.

Ball joint stud size (except LNF) 19.5mm
Ball joint stud size (LNF Only) 20.5mm

 

I have to double down on what TDubb said. The off the shelf ball joints at parts stores are not the right ones for the 08+ SS Cobalts. The ball joint post/stud is larger on the 08+. That could be some of your problem. Check you control arm bushings too.