Growing up in a country where English is not the native language, I always hear people phrase declarative statements in an interrogative form. I'm not sure if it's grammatically correct to do so.
Example in Question Form:
What will he do, I wonder?
Declarative(What I hear from others):
I wonder what will he do.
Based on what I have known all my life, I would phrase it as such:
I wonder what he will do.
... While I am sure that the way I constructed it is correct, I'm not sure if one could phrase it the way they do.