plone.app.discussion/plone/app/discussion/notifications.zcml

<configure
    xmlns="http://namespaces.zope.org/zope"
    xmlns:zcml="http://namespaces.zope.org/zcml"
    i18n_domain="plone.app.discussion">

  <subscriber
      for="plone.app.discussion.interfaces.IComment
           zope.app.container.interfaces.IObjectAddedEvent"
      handler=".comment.notify_user"
      />

  <subscriber
      for="plone.app.discussion.interfaces.IComment
           zope.app.container.interfaces.IObjectAddedEvent"
      handler=".comment.notify_moderator"
      />

</configure>