This article is related to below post where user reported missing ribbon issue after migration from SharePoint 2007 to 2013 version.

https://social.technet.microsoft.com/Forums/en-US/628b9f7b-b1e7-4bb1-b01d-fcb11b252862/ribbons-missing-after-migration

Scenario:

Ribbon not visible on SharePoint List/Library page load. Mostly reported after site migration from 2007 to 2010/2013 version. Also if you have added a content editor web part on this page.

01.<scripttype="text/javascript"src="https://code.jquery.com/jquery-1.11.3.min.js "></script>

02.<scripttype="text/javascript">

03.$(document).ready(function(){

04.var elem = document.getElementById("MSOZoneCell_WebPartWPQ2");

05.           if(elem != null) {

06.                var dummyevent = new Array();

07.                dummyevent["target"] = elem;

08.                dummyevent["srcElement"] = elem;

09.                WpClick(dummyevent);

10.                _ribbonStartInit("Ribbon.Browse", true)

11.            }

12. });

13.</script>