There is always more than one way to skin a cat. My preference is to optimize simplicity and maintainability. Each part can be tested individually and there are no WHERE clauses.

SELECT -- get all employees and required courses

e.EmployeeId,

e.FirstName,

e.LastName,

c.CourseId,

c.CourseName

FROM

#Employee e

CROSS JOIN

#Course c

EXCEPT

SELECT -- remove completed employee courses

e.EmployeeId,

e.FirstName,

e.LastName,

c.CourseId,

c.CourseName

FROM

#Employee e

JOIN

#CourseCompleted cc ON cc.EmployeeId = e.EmployeeId

JOIN

#Course c on cc.CourseId = c.CourseId

ORDER BY

e.EmployeeId

;