On average, how many lines of code should a developer write per day?
I want to know how to answer this question.
LoC is not an accurate way to describe performance. It does not take into account how much work has been done, how much your code base is bloated. http://www.folklore.org/StoryView.py?project=Macintosh&story=Negative_2000_Lines_Of_Code.txt
On some days you won’t get anything, on other days you can collect a few hundred. Depends heavily on the project and the people involved.
How much does he need.
It depends on many factors for which it is impossible to give a general answer. Plus, how do you define "should"? Lines of code are also a poor indicator of progress anyway ...