Undertaker is pushing 50 and his body is destroyed, so "Do you wanna do it?" clearly wasnt a shoot challenge of any sort. He's working an angle, the only question is if Lesnar is in on it.
The fact Undertaker did this interview, completely out of character no less, is the first red flag of 'work'. He doesnt do that stuff. They could have some back door deal with Dana & Brock, and Taker did this 'out of character' interview to give the angle credibility. Buildup for WrestleMania, perhaps.
The sherdog geeks would all die of heart attacks if this were the case, hilarity would ensue to the highest order.