I think the answer is 「４．何かで」 I guess it goes like: たまご りょうり の じょうずな つくりかた を（何かで）読みました。 「何か」is "something" 「で」 is "by" So, it can be by a book or a magazine. The translation of the entire sentence'd be like, "I (did) read something how to cook eggs well." And it implies he/she doesn't remember what it was lol