"It is me again."
Benim is a possesive pronoun, so it acts like an adjective and can't be the subject of a sentence. Ben is first person singular, and can be the subject. The difficult part here is that the verb, "is", is understood in Turkish. It might be easier to imagine saying, "Me, again," and swapping the word order. I know that's not correct grammatically, but practically no one would say, "I, again" in English, even if it's correct.