I have an Xelement which looks like:
<headers batchid="123456" xmlns="http://api.temp.com/ns/">
<header uri="https://api.temp.com/v1.0/headers/147852" id="147852" />
</headers>
I'm trying to read the "uri" attribute. When I tried :
var temp = xmlResponse.Attribute("uri");
it kept return me null.
So I tried:
var temp = xmlResponse.Element("header");
var temp2 = xmlResponse.Element("headers");
and they are also returning null.
What am I doing wrong?

You're ignoring the namespace of the element. Due to the xmlns="...", both the headers and header elements are in a namespace of "http://api.temp.com/ns/". Fortunately, LINQ to XML makes this really easy to fix:
XNamespace ns = "http://api.temp.com/ns/";
var temp = xmlResponse.Element(ns + "headers");
var temp2 = temp.Element(ns + "header");
(Note that the header element is nested within the headers element, hence why I'm calling temp.Element to get at it.)
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