How can I attach modern fixture to knob & tube wiring?
Use a NCVT (non-contact voltage tester) and see which of the two wires alarms when the switch is on. That will be your black/hot wire. If both of the wires alarm, stop, do not pass go, something else is wrong.



For the ground, you don't have one. The safest thing to do is run a whole new wire back to the panel. Anything else is "less than safest".