Please enable Workflow Rule to execute on public comment

Please enable Workflow Rule to execute on public comment

We do not use reply in our organization. All of our agents use public comments. When I try to create a workflow rule, I am not able to execute on Public Comment. My goal is to send an email to the agent (and one additional person) when the agent posts a public comment. I know the agent gets notified if customer posts public comment, but I want a notification to be sent to the agent when the agent puts in a public comment.