My clutch all the sudden has a large space of free play whereas before it had none.

A seal might have popped and you lost fluid. I've had 2 clutch slave cylinder seals fail when the weather has been at or around freezing for an extended period.

Check fluid level, look for leaks, replace what is leaking. If no leaks check the pedal mechanism to make sure nothing worked it's way loose.

Where can I check this? I just bought the car and I'm unfamiliar with the car.

Get familiar here:

http://xenonzcar.com/z31/FSM/1987fsm.php

Your clutch master cylinder is next to the brake master cylinder, opposite the pedals in the engine bay, the clutch slave cylinder is on the passenger side of the transmission. Look for leaks coming from either.