That's not a stupid question, Jenny, I was wondering too. No prob on a pc - there should be a few special characters provided by DL, including undotted ı.
On my Android phone, I went into Settings / Languages and Input / Google Keyboard / Languages, and added the Turkish keyboard from the long list. (I think you have to turn OFF "Use system language"). Then by tapping the "globe" symbol left of the spacebar you can cycle your keyboard through available languages (I have French too). Then - hey presto! - you can type ı and İ. HTH
Hope you have fixed it Jenny. I discovered a couple of omissions in my post above - now fixed in italics. And of course, none of this helps if you want to put an "ı" into a discussion like this working from a PC - you just have to use the "Character Map" app which comes with Windows. If you are on Apple I can't help!
You can add the Turkish keyboard layout on a PC, then the I key gives you the dotless ıI and the apostrophe and quote key gives you the dotted iİ. http://duolingo.wikia.com/wiki/Turkish
Here is a picture of the keyboard layout to see the special letter keys. https://www.microsoft.com/resources/msdn/goglobal/keyboards/kbdtuq.html