"When do you cook rice?"
Translation:Khi nào bạn nấu cơm?
for your information, this does not literally mean the time to cook the rice, but it actually asks when do you start preparing the meal.
I would say this: when khi nào is placed at the end of the sentence, the question indicates past tense (when did the action take place), and when at the beginning like the sentence above, the question indicates future tense (when will the action take place).
So "nấu" is the verb and it needs the "ăn" part only if a certain food is not specified, right? Trying to understand, why there is nơ "ăn" here :)
U use nấu if it goes with another word (cook rice = nấu cơm), it is nấu if its alone