Rule 1. Use a question mark only after a direct question.
Correct: Will you go with me?
Incorrect: I'm asking if you will go with me?
Rule 2a. A question mark replaces a period at the end of a sentence.
Incorrect: Will you go with me?.
Rule 2b. Because of Rule 2a, capitalize the word that follows a question mark.
Some writers choose to overlook this rule in special cases.
Example: Will you go with me? with Joe? with anyone?
Rule 3a. Avoid the common trap of using question marks with indirect questions, which are statements that contain questions. Use a period after an indirect question.
Incorrect: I wonder if he would go with me?
I wonder if he would go with me.
I wonder: Would he go with me?
Rule 3b. Some sentences are statements—or demands—in the form of a question. They are called rhetorical questions because they don't require or expect an answer. Many should be written without question marks.
Why don't you take a break.
Would you kids knock it off.
What wouldn't I do for you!
Rule 4. Use a question mark when a sentence is half statement and half question.
Example: You do care, don't you?
Rule 5a. The placement of question marks with quotation marks follows logic. If a question is within the quoted material, a question mark should be placed inside the quotation marks.
She asked, "Will you still be my friend?"
The question Will you still be my friend? is part of the quotation.
Do you agree with the saying, "All's fair in love and war"?
The question Do you agree with the saying? is outside the quotation.
Rule 5b. If a quoted question ends in midsentence, the question mark replaces a comma.
Example: "Will you still be my friend?" she asked.