Alumni can post comments about an event only if they have accepted the event invitation. Administrators, privileged employees, and event organisers can check the comments from time to time and respond to them as well.
At the top of your dashboard, click the module access icon > Collaboration > Alumni > Event Invitations to open the View event invites page.
Click the event for which you want to check the comments. Comments are displayed at the bottom.
Enter your comment, and then click the Submit button to post.