function findElement(what, where) {
  if (typeof where !== 'object') return null;
  if (what in where) return where[what];
  for (let key in where) {
    let result = findElement(what, where[key]);
    if (result) return result;
  }
  return null;
}

const obj = {
  a: document.createElement('div'),
  b: {
    c: document.createElement('div')
  }
};

console.log(findElement('d', obj));