On a specific question the question which was a duplicate of the question is not visible:
Prior to the current implementation of duplication, questions were simply closed with the duplicate link entered directly into the question.
This is one of those old questions that was closed in that way. Just look a little lower to find the Possible Duplicate link.
While we could reopen and close such questions again so that they use modern duplication you have to ask yourself whether it's really worth the effort. The question has only had 50 or so views in its entire life, though it will probably get a few more now you've linked to it.