可以使用循环嵌套遍历两个数组，比较它们的属性值是否相同，找到匹配的对象后返回答案。以下是示例代码：

function compareArrays(array1, array2, question) {
  let answer = null;
  for (let obj1 of array1) {
    for (let obj2 of array2) {
      if (obj1[question] === obj2[question]) {
        answer = obj1[question];
        break;
      }
    }
    if (answer !== null) { // 如果已找到答案，则退出循环
      break;
    }
  }
  return answer;
}

// 示例用法
let array1 = [{name: "Alice", age:20}, {name: "Bob", age:30}];
let array2 = [{name: "Charlie", age:25}, {name: "David", age:20}];
let question = "age";
let answer = compareArrays(array1, array2, question);
console.log(answer); // 输出结果为20（因为Alice和David的age都是20）