The first sentence is best. It sounds the most natural.

I am a third year student majoring in literature at ..( name of a university) This is fine. I am a third year university student studying literature as my major at ....(name of a univer) This is grammatically correct but wordy. Majoring in something automatically implies you’re studying it. However, the inverse is not always true. For example? I am a third year university student studying literature but majoring in art at… I am a university student and I specialize in literature. Grammatically correct but studying or majoring is more common. You would, however, use specialize to specify something specific with the major. I am a third year university student majoring in literature and specializing in post-war works.

Hi, The first two are great. The third one is grammatically correct, but it is unusual to use the word "specialize" to describe what a college student is studying/majoring in. It's usually used for something more specific, if it exists. For example, "I'm studying education, specializing in American history."

They are correct in the way the sentence is stuctured tho I would like to know more if it is being used in a casual conversation or presented in a resume or CV. There is a specific way to formulate that sentence that would make it seem more profecional. I would like to point out tho that the last sentence is to vauge.