Find the enrollment date for all the tests that have "Pass" result.
SELECT T1.date_of_enrolment FROM Student_Course_Enrolment AS T1 JOIN Student_Tests_Taken AS T2 ON T1.registration_id  =  T2.registration_id WHERE T2.test_result  =  "Pass"
enrollment date refers to date_of_enrolment; tests that have 'Pass' result refers to WHERE test_result = 'Pass'; joining tables refers to JOIN; matching records based on a common field refers to ON T1.some_field = T2.some_field;