Your question is a bit puzzling - do you really want to obtain an xpath expression for each HTML tag?

Usually it's the other way round: You need to extract some specific HTML tags, and use xpath for that.

So the best way to start would be to learn XPath a bit, then look at the HTML page you want to extract stuff from, and write an XPath expression to extract what you need.

Install HTML::TreeBuilder::XPath, experiment with it, and refine your xpath expression until it does what you want.