A. Any of those are correct, depending on what you mean. Why do you come to school? (e.g., to learn? because your mother makes you? Because you want to gain a degree to get a good job?
How do you come to school? (e.g., by bus? in your own car? someone drops you off at school? you ride the train?)
When do you come to school? (On Monday, Wed., and Thursday?, At 8 a.m.? Wh
Yes, all of the above are correct. Usually, when one answers the "When were you late?" question, one would just say, "Monday," or "Last Monday." A time is not usually added, although you might say, "Last Monday. I didn't get there until 8:30."