Question marks are used to show the end of a question. The sentence after the question mark always begins with a capital letter.
Where have you put the release?
If it is used in the middle of a sentence, it is followed either by a word starting with a lower case letter or another punctuation mark, such as an en dash.
“Where now?”, they wonder.
A question mark is not needed after sentences framed as questions out of politeness or common usage:
May I take this opportunity to thank you for your contribution to this project
When a question takes the form of direct speech, the first letter should be capitalised and the whole question put in quotation marks:
“Why are there discrepancies in the count?” she asked