We may just catch one in December, where s the best place to see it from? can we see from pop century or do we have to be closer to the space center launch
You'll want to be facing east. Not sure how well you'll be able to see it from WDW (lights will interfere) but once the shuttle clears the horizon you'll surely see something, weather permitting.
Oh, if you want to travel to get a better view, then by all means head east. Titusville is one choice, Jetty Park at Port Canaveral is another.
Do realize though that zillions of folks go for shuttle launches, so the roads are jammed, and you'll need to leave quite early to get a decent spot.
Then, they can (and do) cancel them at any time for any number of reasons.