你在线吗?
答案正确.
你被插入的-ed 短语干扰了,找不到句子的主干了.
给你解剖一下,抽去...referred to.
The witness suggested that the cheat (should) be put in prison.
其中的 the cheat (who was) referred to. 所(被)提到的/所(被)指认的 骗子
再合起来:
The witness suggested that the cheat (who was) referred to (should) be put in prison.
证人建议要让(他)所指认的那个骗子坐牢.