In AEM 6.3 and above, there is a feature that allows content authors to “Request Publication” or “Request Unpublication.” The option becomes available when the content author does not have replication permission on the page they are currently authoring
When you click on "Manage Publication" it takes you to a page
Now when you click on Publish or Unpublish, then AEM's OOTB Request for Activation or Request for Deactivation workflows gets triggered respectively.
In order to trigger custom workflow on click of manage publication, below are the steps:
1. Go to/libs/cq/gui/content/common/managepublicationwizard/body/items/form/granite:data path and right click and then click on overlay node.