英语关于同位语从句
Do you know the truth that where there is life there is hope ?
～～～～～
请问作为同位语从句这里为啥这里加了THAT还加WHERE

EG, have no idea when he will be back．我不知道他什么时候回来.
He must answer the question whether he agrees to if or not.
他必须回答他是否同意这样一个问题.
此处就没用THAT而单个连词