Microphone doesn't work
On Macbook Air with DuoLingo?
The new website uses a new programming interface for voice/speech and only a few browsers currently support it. One is Chrome so you could try downloading this on your Macbook and you should then get questions to test your speech.
Pete hit the nail on the head. Here's the official word:
Why don't I get speaking exercises anymore?
Speaking exercises on the new website only work on browsers that support the Web Speech API, the most popular being Chrome. Unfortunately, the old speech system was outdated and a burden on our system. If you use the Chrome browser, you will get speaking exercises again.