Formulating a research question is extremely difficult. That's why the teachers have already formulated your main question and the subquestions for you. Next year when you write your 'profielwerkstuk', you are going to be able to choose these questions yourselves.
Main question:
How do your five chosen projects fit in with the sustainable vision of the municipality of Rotterdam?
Subquestions:
What does sustainability mean to you?
What is the municipality of Rotterdam's vision on sustainability?
What did you prepare for your sustainable city walk?
Which projects have you chosen and why?
Why are the projects sustainable?
What is the connection between the projects and the subject Geography?
Which project appeals to you most and why?
The idea is that you first answer all the subquestions and that the answers of all the subquestions together will ultimately lead to the answer on the mainquestion.