Wow this is alot more complicated looking than 2.9 (I have 3.01 on my test server).
When you say course to clarify do you mean you have modules containing courses? if so then looking at this it is done via the Activity completion but the course completion must first be set against each course(activity)
Apologies for below but they do not appear to have updated the pages for 3.0
Condition:Activity completion
(These settings are collapsed by default.)
 Activity completion settings expanded |
Tick the boxes of the activities you wish to count towards completion of the course. (You need to have Activity completion enabled to be able to do this. You can decide whether ALL of the activities must be completed or ANY one of them.
Condition:Completion of other courses
(These settings are collapsed by default.)
 Settings when no other courses have course completion enabled |  Settings when course completion is enabled in one or more other courses |
This setting allows you to make "the completion of another course" as a condition for completing the course you are currently working in. This does not block the student from your current course; it simply means that the current course will not be marked complete until the first course has been marked complete. Thus, completion of the current course is dependent upon completion of an earlier course. Just select one or more courses in the "Courses available box". Note: Once you have selected a course, it's not currently possible to remove it. See MDL-27114