He wanted a job one he had never experienced before.把the 去掉后one 做a job 的同位语
one 后面的一大溜做定语修饰one
He wanted a job that he had never experienced before 换成that 后就不存在什么同位语
that 引导的是a job 的定语从句
上面两种情况明白了之后
至于为什么不用the one
因为the one 是特指,而a job 是泛指,两者应该统一