What is harder to establish is weather the productivity revolution that businessmen assume they are presiding over is for real.

【翻译】更难确定的是，企业家们认为自己正在主导的生产力革命是不是认真严肃的。

【分析】

1. What is harder to establish（主语从句） is （系动词）weather the productivity revolution that businessmen assume they are presiding over is for real.（表语从句）

2.  weather the productivity revolution （主语）that businessmen assume （“混杂式定语从句”,定语从句也是assume 的宾语）they are presiding over（定语从句修饰productivity revolution） is（系动词） for real.（表语）

3. for real 是一个“习语”。意为“真实的；认真的；严肃的；果有其事的”。