What is YUI equivalent to below JavaScript code?
document.getElementById("myDiv").removeAttribute("id");
I'm guessing you're meaning YUI2. But in case you meant YUI3, it's exactly like the DOM method:
Y.one('#myDiv').removeAttribute('someAttribute');
You can read a list of all Y.Node methods in the API docs: http://yuilibrary.com/yui/docs/api/classes/Node.html