Hi Agnes

Seminar booking admin request: this is sent to people who have been selected as an administrative approver - either through the event role or activity level through two stage approval

Seminar booking request: this is sent to all people who are required to approve the seminar booking so could be managers and administrative approvers

Seminar booking role request : this is sent to users that are selected who are in the roles specified in event role approval.. There may be several users in the approval role for the seminar so when the event is setup you have the option to select the users for the specific event . This is who receive this notification.

Hopefully that helps.