Re: "Do you think when to start?" or "When do you think to start?"
I found the first sentence in a handout by a junior high school teacher in Japan, at which my daughter studies. It has no context. It is used to explain the use of "what to buy", "how to drive a car", and so on. Something seems to be wrong with the first one. So I wrote the second one, but it is still strange...
I suppose the teacher wants to mean "When should we start? Are thinking of that?".
What do you say in that case?