Hi Amjad
For me there are 3 things that make OpenUI5 a good javascript libray for an existing enterprise backend developer to learn.
1. the ease in which you can consume data from a backend system via the OData Model - integrating with SAP is very complicated and hard to scale
2. there are a lot of controls which abstracts the need for you to know or care about the underlying HTML and DOM, controls provide a consistent look and feel and they are extensible meaning you can easily make them look and behave how you want
3, the application structure provided in the MVC paradigm, without this structure your applications will be hard to extend and support
These 3 concepts should be familar to an ABAP Webdynpro who wants to learn OpenUI5, for those developers I would say you shouldnt learn JQuery first you should try and avoid it initially. Focus on the structure of your application and use the OpenUI5 provided controls and global APIs as much as possible .
jQuery API's abstracts the HTML DOM, the OpenUI5 core library API's abstracts jQuery, OpenUI5 controls API abstract the OpenUI5 core libary.
eg
var oButton = sap.ui.getCore().byId('myButton');
var oButtonDom = oButton.getDomRef(); //>> equiv jQuery.sap.domById(this.getId()) >> equiv to jQuery('#' + id);
Cheers
JSP