For most edX courses, there are no firm prerequisites. In other words, you won't be blocked from enrolling without completing the prerequisites.
If a course has any prerequisites, they are listed on the course introduction page under At a glance.
These prerequisites are recommendations to ensure your success in the course, but in most cases this is not a strict requirement. For advanced capstone courses (such as the final course in a MicroMasters program), the course team may not allow learners who have not completed the required program courses to enroll.