When to use ’啦‘ and "嘛‘？
啦 is not truly a question ending. Actually 了 is. 
 E.g. 你刚才去哪了？ Where did you go just now? 
 However Chinese people do like to use 啦 instead of 了 to ask questions. Maybe it sounds cuter? So the example becomes 
 你刚才去哪啦？It's just a verbal use. 

In question sentences, 嘛 can be used to substitute 什么 as a question ending. E.g. 你在干嘛？What are you doing now? instead of 你在干什么？I cannot think of any question else that ends with 嘛.

 BTW these two characters are also widely used for acting cute...
E.g. 好了啦！ 干嘛啦！common in girlish talks.