those reviewers（主语） ,could be trusted（谓语被动形式） to know （表目的）what they were about（做know的对象）.
倒过来的意思是 somebody trusts the reviewers to know what they were about. 根据你给出的中文意思，they 应该是指reviewer，其实如果无上下文的话，they也可以理解为sb。
能力不足，有说的不对的地方，楼下帮忙纠正，共同学习。作者: sanbi 时间: 10-8-13 09:29
提示: 作者被禁止或删除 内容自动屏蔽作者: tyropapa 时间: 10-8-13 11:05
[Even] those reviewers (who wore their learning lightly) , [like George Bernard Show and Ernest Newman ,] could be trusted to know what they were about.
who wore their learning [lightly] 后置定语从句修饰reviewers，其中lightly是状语修饰wear(释义见下或者自己查字典)
wear:If you wear a particular expression, that expression is on your face and shows the emotions that you are feeling.
like George Bernard Show and Ernest Newman 插入语，示例reviewers
主结构见蓝色粗体部分
could be trusted to know what they were about.
查查trust的释义“If you trust someone to do something, you believe that they will do it.”
被动语态还原成正常格式就是(people) could trust those reviewers to know what they were about.
they很自然的是指those reviewers