Actually the polite way to say DOCHI, is DOCHIRA.
When asking the question "which one?" and there are TWO options, DOCHIRA is used.
DONO means "which" as well, but refers to more than two options.
So, let's say a boy won the prize, and his friend asks "which one did you win?" out of the many prizes that are displayed, the friend would say *Dono sho o totano? *. If there were only TWO prizes, he would ask *Dochi or Dochira no sho o totano?*
Or, when you want to ask WHICH station to get off "At what station do I get off?", it's *DONO eki de orirunodesuka*, in Japanese.
To ask "where is~?", you cannot use DONO to replace DOKO. So, *DONO desuka? *instead of *DOKO desuka *is incorrect. :shock: