如何判断网站是否使用JSON或XML以及如何提取该数据？

I cannot for the life of me find any resources for the above. What I'm attempting to do is discover if the website I am looking at uses JSON or XML, and then to pull that data. I understand that is a complicated question, so if anyone has any resources I would appreciate it. What I have now is a UITableViewController and in its initWithStyle: method I include my own method call of "fetch feed." My fetch feed method looks like so:I cannot for the life of me find any resources