1. Yes, this diagram is correct.
2. Each line is supposed to be a record in a table. When an event is added, a number of records are added equal to the cross product of the number of Employees and Trainings selected in the Event.
3. In my mind, the employees would be selected individually. There is not really a better way to group the employees logically. So our Training Coordinator would select the Group (G1) and the Related Employees (E1, E2, E3, E4). Then the records would be created based on the cross product of the Trainings in the Group and the Employees selected.