Can you tell me how to critically reflect upon a learning tool — wikipedia.

To be critical would be to think about something from many angles and contexts. In this sense, you can look at Wikipedia through an academic lens of whether or not it meets the standards of a research tool and learning tool overall. Write about all the pluses and minuses of the website, or rather database. You can come to a conclusion through your investigation, but make sure you base your assessment on facts, logic, and practical application.