Often in writing you see question marks following sentences that begin with I wonder or Guess.
With I wonder sentences, you are stating that you don’t know the answer to something—but you are not asking a question. I wonder how long my flight is going to be delayed is not asking for information. It’s a declarative statement saying you don’t know how much longer you will be frothing at the mouth at JFK or LAX. It’s another way to say, I am wondering. You wouldn’t use a question mark after that, would you?
Guess where I was born similarly is not a question. It is a statement, a command, telling your audience to figure out where your birthplace was.
So hold your question marks for actual questions. Most will start with who, what, where, when, why, how much, how many, would you, could you, can you, have you.