When do all of John Wen's certifications expire?
SELECT T2.CertificationExpires  FROM physician AS T1 JOIN trained_in AS T2 ON T1.employeeid   =   T2.physician JOIN procedures AS T3 ON T3.code   =   T2.treatment WHERE T1.name   =   "John Wen"
certifications expire refers to CertificationExpires; all of John Wen's certifications refers to filtering WHERE T1.name = \"John Wen\"; joining tables to find related data;