I picked up my strat today, started jamming and noticed that the tone knob for the neck position is broken.

It turns all the way around, and is very loose.

Should I take it into the shop or is there something I can do to fix it?
dont take it to the shop.

remove the pickguard, inspect damage, report back and we'll help you.

just try to find out what exactly is wrong there.

Is it the knob itself of the variable resistor it sits on that is loose?
if you just got it take it back to where you got it and tell them to take a look at it. then you dont risk messing it up and if it is really messed up the shop will know what to do and not make it worse.
to above:

unless you have your hands growing out of your arse...do it yourself.
It's the knob itself. As in, the little round thing with numbers on it.

When I take it off, the metal rod underneath turns perfectly. But even if I put different knobs on it, I get the same problem. I don't get it.
tighten the clamps on the inner side of the knob (might be a grip problem). another thing that could have happened, is that the two rods that are underdeath have been bent (happened to me). it would be very hard to bend the back if this is the issue. i tried to, but what happened was that one of the two parallel rods just broke off.

i havent bothered fixing it...my last tone knob is just a rod now, but it works, so i dont care.