gistfile1.js

var data = [
  {
    name: 'Nadav',
    school: 'Weber',
    interest: 'Jazz'
  },
    {
    name: 'Noy',
    school: 'Epstein'
  },
    {
    name: 'Noa',
    school: 'Something'
  },
];

var combineKeys = function(data) {
  return data.map(obj => Object.keys(obj))
    .reduce((prev, current) => 
      prev.concat(current.filter((key) => 
        prev.indexOf(key) < 0))
  );
};

console.log(combineKeys(data));