How can I get the data-id attribute?

To get the contents of the attribute data-id (like in <a data-id="123">link</a>) you have to use

$(this).attr("data-id") // will return the string "123"

or .data() (if you use newer jQuery >= 1.4.3)

$(this).data("id") // will return the number 123

and the part after data- must be lowercase, e.g. data-idNum will not work, but data-idnum will.