Actually i am building nixie tube clock controlled by arduino nano and switching transistors mpsa42 and mpsa92.
and need to select anode current limiting resistor. I know resistor values but i am confused with there wattage.
That's not too difficult:
The typical anode current of a Nixie tube is around 2mA. I assume the resistor value is correct for this application, so the current will be. If not, your nixies may have a short live.
So if you know your resistor value, the power rating is I^2 * R
-> about 60mW for a 15k Resistor
Any common MiniMelf, Melf or standard size THT resistor should do the job. Voltage drop across the resistor is calculated by I * R (-> 30V for my example), so not a big deal here.