Maybe. It's currently just a safer bet to learn and use Python. Easier to get a job after you fail getting your next grant. I have so far seen zero Julia job ads. Hell, I see more e.g. Haskell and Fortran job ads than Julia.
or learn both and have the convenience+speed of Julia for scientific work? Speaking from my experience here as a bioengineering PhD student. The Julia learning curve is low enough for an experienced Python/scipy user to switch over fairly swiftly.
edit: also, I would be very surprised if you had seen any Julia job ads, v1.0 hasn't been released yet. Doesn't mean it can't make my scientific life easier in the meanwhile.
Julia gives you such a competitive advantage that you can easily position yourself into a great career. It worked out really well for me. Of course YMMV, but having a much greater productivity and software quality never hurts.
edit: also, I would be very surprised if you had seen any Julia job ads, v1.0 hasn't been released yet. Doesn't mean it can't make my scientific life easier in the meanwhile.