假设Rober = 张小三,his father = 张三。
原文Robert wanted his father to know how much to love his father.
=张小三想让张三知道(张三应)如何爱他的(张三的)父亲。
改文:Robert wanted his father to know how much he loved his father.
=张小三想让张三知道自己(张小三)有多爱他(张三)。
结论:
原文本身没什么问题:儿子要老子知道如何去爱老子的老子(儿子的爷爷),根据提供的改文来看,原文属于意思表述失误--儿子不是要老子知道如何去爱老子的老子,而是想让他老子知道自己有多么爱他。哈哈