I am using SpringFramework Couchbase library to construct N1QL queries.
I am using createSelectFromForEntity
Where do I specify the names of fields I want returned to return ?

When you say SpringFramework Couchbase library, are you referring to Spring Data Couchbase?

If so, there are a number of examples in the documentation on the Spring site, which a number of Couchbase people contribute to.

Spring Data is the Spring sub-project for systems like Couchbase and you’ll often use the Spring Expression Language to specify your N1QL query predicates. Projections (specifying fields to be returned) are also covered there in the docs.