Hi João,
Smart digging there!
You assume right, ElementKey is the internal unique key of the element, which is used by Service Studio, among other things, to let you rename an element without breaking your code (unlike what happens in traditional coding languages). Currently it's not possible to extract this information for all elements.
This being said, if I'm not mistaken, there are some places where this is recorded, e.g. for public elements that are referenced they might be on the Espace_Reference system entity, some client side element keys might also be dumped on the generated code when the application is in debug mode. All this, of course, is not supported, so do it at your own risk.
In any case there is a great idea regarding links to elements inside Service Studio, that you might want to vote on.
Cheers,
Tiago Simões