"Which date is it today?"
Translation:Vilket datum är det i dag?
But the question was specifically "Which" not "What" so Vad är dagens datum? would not be right in this case, right? (FYI: Saying "Which date is it today?" sounds odd in English. Saying "What is today's date?" makes more sense. Although, most people, at least in Canada and the US, would say "What is the date today?")