* It is a noun referring to a part of the psyche in Freudian psychoanalysis.
* It is not a proper noun like a person's name or a specific place.
However, it might be capitalized if it is used as part of a specific title or heading, like:
* The Superego and Its Relation to Guilt
* A Study of the Superego in Adolescent Development
So, in most cases, you would write "superego" in lowercase. But if it is part of a title, check the context to see if capitalization is necessary.