In a preveious request to have closed questions identified, the answer states in conclusion:
Closed question status isn't indicated anywhere
Update: the next update should exclude closed questions from the questions list. While we do plan to have more complete support for closed questions in the near-ish future, I consider this to be the fix for this bug. I've now marked it status-completed.
As the answer was posted in Feb 2014, it looks like this fix has regressed or been changed. This filtering and/or indication of closed status isn't happening on v 1.1.0.94 of the iOS app. You can see by searching for yosemite on Ask Different between now and general release of that OS to get a good mix of questions that are on hold and closed. Tapping the question does then show in the footer the correct closed/hold status, but it's not clear from the main list view.
Please either filter closed questions from the list of questions when browsing on a site or indicate their closed status by pretending the subject line with [hold] or [closed] to clearly indicate their status.