Where can I approve or reject a Training Task when I have a role as a Task Supervisor in a Training?

The role of the Task Supervisor is to make sure the Tasks in the training have been carried out correctly.  
The Task Supervisor can accept or reject a Task of a Trainee when the Trainee has marked the Task as done as it goes into status 'Pending Approval':

Please note that if you intend to remove the Task Supervisor, the supervisor should approve any pending tasks before removal. Otherwise, the status remains locked until approval is received.