"Hvilken én er din sandwich?"
Translation:Which one is your sandwich?
You can change your keyboard on PC by going to Control Panel -> Clock, Language and Region -> Language -> Add a Language, then in the list, select "Danish" and you should be able to alternate between keyboards using the windows key + Spacebar (note this is using Windows 8.1, I have a feeling the process is similar, if I remember correctly, on Windows 7)
You can then add the accent over the é using the key to the left of the backspace (for me, using a UK keyboard, that's =) and then pressing "E"
Is "hvilken én" commonly used? It sounds so English to me, first time I hear it in any other Germanic language.