I am running SharePoint 2013 compatibility mode. I have Content Approval turned on for my Site Pages library. When I go to a page and click Submit on the Publish tab of the ribbon, SharePoint temporarily displays a message that says "Submitting page for approval" followed by another temporary message that says "Page submitted for approval". Then there's a yellow bar across the top of the page that says "Status: Waiting for approval". But I never see the workflow initiation box where I can enter any workflow parameters and I don't receive any e-mail notification that the page was submitted for approval. I'm a member of the site Owners group (with Full Control permissions) and a member of the site Approvers group (with Approve permissions). Why didn't the workflow initiation box appear and is the OOTB Publishing Approval workflow supposed to automatically send an e-mail to the Approvers? Thanks.
Turning on Content approval will not activate the workflow, it will only activate content approval on document library and Approver group will have access to approve the site pages.
You will need to add approval workflow by going into workflow settings of site pages library.
Below is the reference to configure approval workflow for document library. https://www.webucator.com/tutorial/advanced-microsoft-sharepoint/content-approval/enabling-using-sharepoint-approval-workflow-exercise.cfm