Use name(). (Find docs for newer versions of the XPath language here.)
Here are modified versions of your example:
Works in XPath 2.0+ only:
//element/*[@id='elid']/name()
Works in XPath 1.0 and 2.0+*:
name(//element/*[@id='elid'])
*If using 2.0+, the expression //element/*[@id='elid'] must only return one element. Otherwise you’ll get an error like A sequence of more than one item is not allowed as the first argument of fn:name()
You could also use local-name() which returns the local part of the expanded name (without any namespace prefix).