使用此代码：

let parentArr = [
  {
    subjectID: '2',
    studentList: [ [Object], [Object] ],
    subjectTitle: 'Physics',
    subjectLevel: 'IGCSE Level',
    syllabusCode: '0625',
    subjectGroup: 'Humanities'
  }
]

let newArr = [] ;
parentArr.forEach((parent)=>{
  parent.studentList.forEach((child)=>{
    newArr.push({
    subjectID: parent.subjectID,
    studentID: child.studentID,
    subjectTitle: parent.subjectTitle,
    subjectLevel: parent.subjectLevel,
    syllabusCode: parent.syllabusCode,
    subjectGroup: parent.subjectGroup,
    })
  })
})

Yoy可以使用此代码

const arr = [
  {
    subjectID: '2',
    studentList: [ {"name":"xyz","studentID":2},
    {"name":"abc","studentID":3} ],
    subjectTitle: 'Physics',
    subjectLevel: 'IGCSE Level',
    syllabusCode: '0625',
    subjectGroup: 'Humanities'
  }
]
var arr1 = []

for (var parent = 0;parent< arr.length;parent++){
        for (var children = 0; children< arr[parent].studentList.length; children++){
        arr1.push(
          {
      subjectID: arr[parent].subjectID,
      studentID: arr[parent].studentList[children].studentID,// Here studentID is assumed as a key of student ID you need to replace it with your key
      subjectTitle: arr[parent].subjectTitle,
      subjectLevel: arr[parent].subjectLevel,
      syllabusCode: arr[parent].syllabusCode,
      subjectGroup: arr[parent].subjectGroup,
      }
    )   

}
}
console.log(arr1)
// Now you can insert the arr1 into SQL