didn't 只否定know，它管不着 as his friends did，所以，“他的朋友知道（did）”。

know 的宾语是how to make money in a short time。

由于宾语较长，为了句子匀称，把“比较状语从句”提前。此外，提前的目的也是为了对比：“他不知道”--“他的朋友知道”。

He didn't know, as his friends did, how to make money in a short time.

=He didn't how to make money in a short time as his friends knew how to make money in a short time

（备注：as his friend did=as his friends knew how to make money in a short time,  即did=knew how to make money in a short time)

参考译文：他不知道像他的朋友们那样如何在短时间赚钱（意思就是，他的朋友们知道如何在短时间赚钱，但是他不知道如何在短时间赚钱）

He didn't know, as his friends did, how to make money in a short time.

原句子语序为：He didn't know how to make money in a short time as his friends did.(as引导状语状语提前了，并把原来句子的谓语didn't know和宾语how to make money in a short time分隔开来。）