how to keep their mind on what they are doing by making it do the work without which no profit can be earned.
这不是完整的句子。严格说，这是一个 how to do sth. ，是一个名词性词组。

1. what they are doing 是 on 的宾语。
2. by making it do the work without which no profit can be earned，是方式状语。
3. it  指前文的 what they are doing （他们所做的事儿），do the work  “有成效”。
4. without which no profit can be earned， 是 the work 的定语从句。