"Is it you?"
Translation:Er det dig?
"Dig" is the second person singular accusative (the object of the sentence, such as "me" or "her" in English). Used when talking to just one person: "Jeg elsker dig" = I love you (speaking to one person)
"Jer" is the second person plural accusative. Used when talking to 2 or more people: "Jeg elsker jer" = I love you (Talking to a 2 or more people)