あなたは大学時代どのくらい勉強しましたか？って英語でなんて言うの？

You may try the open question form: "How much effort....?" or the closed question form: "Did you study hard...?" As with all open question forms, this way you are more likely to get a detailed and interesting response compared with the closed question form.
A: "Did you study hard at university?"
B: "Not at all."

If you wanted to ask someone how much they studied when they were in college, you could ask any of the following: "How did you study at college?", "How often did you study whilst you were attending college?" or "How much effort did you put into your work when you were at college?". All three of these questions allow you to direct ask someone who much they studied when they were at college.

When you were in college, how did you study.
This means that you would like to know if they had a study plan. For example: study 2 hours a day.
When you were in college, did you have a lot of work load.
This means you would like to know if you have to study a lot when you are in college for you to pass.
Work load includes your course work, tests, assignments etc.

How much time did you spend studying when you were in college?
Was college easy or challenging? Did you have to study much when you were in college?

If you study hard and do alot of work then we can also call this to study 'alot' meaning you get alot of work done and achieved

In England, college is what we go to at the age of 16-18 years old. After that, we go to University (which is often called college in America). You could ask "How much did you study" but this is quite vague, as it doesn't specify whether they are including lecture time and revision time, or just revision time. The second sentence is a little more specific, just 'revision time'.

If you want to ask someone how much they studied when they were in college, you can say:
"How much did you study while in college?"
"Did you study a lot at college?"
"Did you spend a lot of time studying in college?"