Is there a way to repair the splines where the lug bolt go? or am i gunna have to replace the whole spindle?

 

You can press them out. Not just the splines but the wheel bearing and other parts. I remember finding a thread on how to press them out to remove them yourself. It's a pain. It would probably be better just to remove the caliper disc and then take the knuckle to a machine shop and pay them to press them out so you can replace the splines. Or just buy a new knuckle. It would probably be cheaper and a lot easier than all that work.

 

The part that the lug stud sits in is called the "hub". This part is pressed out and back in when you replace a wheel bearing. If the splines on the hub will no longer hold a lug stud correctly, you'll need another hub. You could buy one new, or get a working one off a junkyard car but you'll have to buy the whole spindle if you can't press it out at the junkyard.

If you get a used one, make sure the smooth part is free of wear or damage. If it is worn down, it won't seat in the wheel bearing race correctly.