Lets see this sentence:
My mom told me I shouldn't go there, I think I should do what my mom told me.
In this case we are using the word what because my mom told me only one thing about the topic we are talking about. (This is the same as we do in my native language.)
But should I use which when I am referring only one thing from a collection?
But when I am typing something which is not a predefined question then Cortana doesn't even try to answer it
Here I have a lot of possibility to type what I want, but I typed one particular sentence. Is this grammatically right or in English we always refer with the word what?
In my language if we would use the word what then the sentence would mean that I can type only one not predefined question (because only one exist) and Cortana doesn't want to answer that one for me. With the word which it would mean that there are more than one not predefined question, and I typed one of them.