Aside from handling requests, it is also of importance to regularly monitor the progress of your trainees. You can do this in the coaching environment by clicking on the 'Coachee progress' tab. Here you can see which trainees have not yet started, are on schedule, are behind on schedule, finished the program or if someone has missed a deadline.
If you spot a specific trainee that is lagging behind or not active (enough) it would be best to discuss this with the trainee in question. You can also contact the administrator of the program about this.
Be advised: A situation could arise where all your trainees are on schedule but you have not yet received requests. This is most likely because not all exercises are set on being 'coachable'. So it could be that the trainee is actually training but the exercises are not configured to be coachable (which prevents the coach from seeing the actual recording).
Info: Information about the utility of whether or not to make a roleplay 'coachable' can be found here.