So tonight I bought some slovacek sausage sausage (The BBQ kind that comes in a box at HEB) to cook for everyone tomorrow.

What is the best way to prepare this? Is it precooked?

Um, shouldn't it say on the box if it's pre-cooked?

My parents like to use a smoker of some kind, but that's about all I know.

Yeah I went and looked at the box and it is stamped on the side...doh.

A smoker or some other form of outdoor cooking using indirect heat is best. But if you're restricted to cooking inside, you can:
#1) wrap them in foil and bake them in the oven
#2) put 'em in a deep saute pan with enough water to cover, then simmer them until the water's gone, or
#3) pan-fry them for a couple of minutes on each side.
If it were me, I'd go with #2.