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.
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. For the subquestions you use (internet)sources to look up the answers, for the main question you use the information from the subquestions and therefore no new information.
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 see and learn during the for your sustainable city walk?
Which projects have you chosen and why are the projects sustainable?
If you have read these questions you can go to step 3 (you don't have to answer the questions yet).