I think I would call Devi Subhadra. Quite contrary to what the serial shows us, Subhadra was always under the protection and care of her elder brothers Krishna and Balarama. They surely won't let Subhadra meet a total stranger like me, so they themselves will also come.
Then to abide by the rules of the boon (can only ask Subhadra a question), I will ask her to tell me pastimes of Krishna, pastimes of Balarama, and pastimes of Krishna, Balarama, and Subhadra
The answer: sure.
But half way through they will all be fixed in divine ecstasy on these glorious pastimes and unable to continue or move. I will take darshan and serve them as Jagganath, Baladeva, and Subhadra for the rest of my life :D