Proper grammar for a question that ends with a colon depends on the structure of the question. Generally, when ending a sentence with a colon, the sentence should form a complete grammatical statement before the colon. Questions most commonly end with a question mark, so when adding a colon it is usually to indicate that the following sentence is an explanation, elaboration, or additional thought on the previous sentence.
Here is an example of the correct grammar for a sentence ending with a colon:
I asked for the book: the clerk said it was out of stock.
In this example, the sentence before the colon is a complete grammatical statement (the question: I asked for the book). After the colon is an explanation or elaboration on the question (the clerk said it was out of stock).
If you are unsure whether or not your sentence is grammatical, you can use a grammar checker like Grammarly to help you identify any errors and make corrections. You could also consult online resources such as the Purdue Online Writing Lab for more detailed explanations of how to use colons in sentences.
