A simple answer is not possible in this format, however,
Given that you already have a Profile, when you add a WorkExperience you will need to manually set the ‘profile_id’ from Profile. The same kind of thing for Assignments.work_experience_id. This should be set in actionCreate of the individual controller.
Getting the related collection would involve relations and using model()->[b]with(‘xxx’)[/]->findAll();
Under Profile: you can add WorkExper. You would have to got each WorkExper to enter individual assignments. Search for update/Create two models on one form.