"Dompter un djinn me doterait de pouvoirs immenses. Ce qui pourrait me servir, un de ces jours."
I suppose that the second sentence means something along the lines of:
" ... could prove useful to me one of these days."
But I’m not sure how to interpret the "Ce qui" part. I have seen a couple of similar sentences that start with "Ce qui", and I wonder if some phrase is omitted at the top?