I don't know 和 I have no idea是同义短句,所以可以改成 I have no idea how to help him.
how to help him的意思是how do you help him=你怎样帮助他,用什么方法帮助他.how I can help him的意思是how can you help him=你可以怎样帮助他.实际上两个意思是一样的,也是同义短句,故可说I don't know how I can help him.
T10次的句子不对.What should I do to help him是一句话,如果前面加上I have no idea的话,这句话就变成了一句话里的一句话,是套句,所以,应该说,I have no idea what I should do to help him.What这类的句子里,如果what是一句话的开头,就应该将I后来的should放到I前面；如果what并不是句子的开头,则should应该在I后面.以此类推.语法上对这一现象肯定有专门的名词解释,我只是常用英文,知道一句话该怎样说才符合习惯.