Objects such as tables aren't really owned by a user. They are owned by a particular schema. Schemas are owned by users.
You can find out what schemas there are by querying the database's system schema view:
SELECT *
FROM <your database name>.Sys.schemas
The principal_id value corrosponds to the principal_id of a database user, which you can find in the database's system database principal view:
SELECT *
FROM <your database name>.Sys.Database_principals
I hope this helps.