Mistakes will always be made in French, and now you can learn from them.
Wrong: Demander une question
Right: Poser une question
Explanation: The French verb demander has several tricky aspects to it. Perhaps most importantly, it is a faux ami - it doesn't mean "to demand," but rather "to ask":
Il m'a demandé pourquoi.
He asked me why.
Demander quelque chose à quelqu'un means "to ask someone for something." Note that in French there is no preposition in front of the thing being asked for, but there is a preposition in front of the person being asked:
Je vais demander un stylo à Michel.
I'm going to ask Michel for a pen.
And finally, demander can't be used with the word question - "to ask a question" in French is poser une question:
Puis-je te poser une question ?
Can I ask you a question?
Other ways to say "ask a question" in French are adresser une question (à quelqu'un) and formuler une question.
Related lessons:
Verbs with prepositions
Faux amis
Conjugations for demander

