SELECT DISTINCT emp FROM EmpSkills s WHERE NOT exists(SELECT skill FROM skills WHERE skill NOT IN
  (SELECT skill FROM EmpSkills Es2 WHERE Es2.emp = s.emp));

SELECT DISTINCT emp
  FROM EmpSkills  ES1
 WHERE NOT EXISTS
        (SELECT skill
           FROM Skills
         EXCEPT
         SELECT skill
           FROM EmpSkills ES2
          WHERE ES1.emp = ES2.emp);