See tooltip on touch screen devices
There's no such generic method because tooltips are not "native" to the web - they're implemented by web sites using generic means. Not every web site will create them the same way, and as such there's no generic method.

In this case Stackoverflow uses a jQuery-based popup system that attaches to event handlers for the mouse (for example the mouseover event). For touch based systems web pages should take advantage of touch events or similar to provide an alternative to users on touch screen devices.