Your manager tells you? Or, higher up the career ladder, whatever is most urgent for the best-paying customer? Like, I know what's on the list to finish for the next multi-million-dollar payout from a major customer, but how my work contributes to it, compared to work done by 20+ other people involved in dev, operations, qa, deployment, customer negotiations, etc.? Who the fuck knows? Best I can estimate is how much it'll cost the company if I fail to deliver my piece on time.