Capacitive power supply - Bleeding resistor reliability considerations
When surge testing, the X2 capacitor will shunt the bleed resistor significantly so it won't see anything like 2kV. However, the resistor should have an adequate voltage rating to withstand full ac mains voltage as if it were connected directly across the incoming ac power.

You need to choose a resistor that can withstand the peak ac voltage and, if necessary, put two resistors in series to exceed the limit by a decent margin.

If you have any doubts about the 2 kV testing then use a sim tool like LTSpice to see what the peak could be.

I would also consider it proper to have a fuse in series with the ac feed to the voltage reducer if it connects directly to line.