This false friend began his tale with many artful speeches to the duke,such as that by the laws of friendship he ought to conceal what he was going to reveal,but that the gracious favour the duke had shown him,and the duty he owed his grace,urged him to tell that which else no worldly good should draw from him. that作指示代词，指代上文提到的他即将揭露的真相，which引导定语从句作draw的宾语，所以这句话可以改写成 urged him to tell the truth which no other worldly good should draw from him.分析的是正确的。

大致意思：这位虚伪的朋友一开始油嘴滑舌地向公爵说了一大堆话来编他的故事，比如什么按照友谊的原则，他本应隐瞒要揭露的一切，但公爵对他的恩泽以及他欠公爵的人情又使他有责任说出事情的真相，而这个真相世界上再没有第二个人能从他这儿获得到了。

红色字体的翻译的可能不准确，目前还在斟酌，希望其他老师一起讨论指导。