It depends on which character set is set. By default, the @ on the Mac is accessible with the Swiss-German keyboard of the key combination "alt" and "g" key. If you want a different country setting, you can change it on the iPad as follows: -> System settings -> General --> Keyboard > Keyboards -> Add keyboard.
You have to look up where to find the @ in English or French, I don't know that for sure.

That's stupid. I don't know the keyboard, but basically the @ sign depends on your keyboard setting. If a CH/DE keyboard is set, the @ should be possible with the key combination Ctrl and Alt and the 2. Since the Alt key has two functions according to the product image, it will probably be necessary to press the Fn key as well. The Fn key is a function key with which you can switch between the two functions of a key. So try the following: Ctrl and Fn and Alt and 2nd (sounds stupid, I know) Hope that works...