The sentence that uses punctuation correctly is: "Didn't you say I could go?" asked Ben.
However, since that exact option isn't among those you've provided, the closest correct option in your list would be: "Didn't you say I could go?" Ask Ben.
If you want to format it properly as a full sentence, it should read: "Didn't you say I could go?" asked Ben.
Make sure to use lowercase for "asked" if it follows the quote in the same sentence.