users = [
  {"name": "Tom", "skills": {"Python", "Java", "C++"}},
  {"name": "Join", "skills": {"Python", "Java"}},
  {"name": "Gaia", "skills": {"Java", "C++", "SQL"}}
]

skills_sets = (user['skills'] for user in users)
common_skills = set.intersection(*skills_sets)
print(common_skills)