Can B

Yes, it has to be Can B.

Let's trace through the logic.

Suppose the geek you asked is the liar. That means the other geek tells the truth. The geek you asked said, "Can A." And that's a lie. So the other geek would really have said, "Can B." And that's the truth.

It also works the other way. If the geek you asked tells the truth, that means that the other geek would really have said, "Can A." But that other geek is the liar, so the skateboard must be in Can B.