Two-wire Conductivity Sensor and Arduino Hook-up?
It depends on the conductivity of the liquid which it is going to be placed/submerged to. For example if the liquid is highly conductive(ex. saltwater), then a 10k Ohms resistor should be fine. But if the liquid conductivity is low(ex. tap water), then its best to measure the output voltage of one lead with respect to the Arduino's ground to be sure what value of resistor to apply to or if there is no resistor needed at all.

But generally if you are going to supply it with 5 Volts, it should be fine to connect it with the Arduino's Analog inputs directly as the operating voltage of the Arduino itself is also 5 Volts.

Cheers!