What is the document date for the project with document "King Book"?
SELECT T2.Document_Date FROM Projects AS T1 JOIN Documents AS T2 ON T1.project_id   =   T2.project_id WHERE T2.document_name   =   "King Book"
document date for project refers to Document_Date; document name 'King Book' refers to document_name = 'King Book'; join projects and documents on project_id.