Should I use a comma before "who" in this sentence, or can it be written without that comma?
Which of the following is correctly written as far as its comma (or lack of comma) is concerned?
People who love their jobs can easily excel in their fields of work than those, who put salary on the first place.
People who love their jobs can easily excel in their fields of work than those who put salary on the first place.
I have read that we should only put comma before who when it adds extra information, but here I think who begins an essential part of sentence necessary for fully understanding it.
The most literal translation of your example which has valid syntax and semantics and is reasonably idiomatic would be something like:
People who love their jobs can more easily excel in their fields of work than those who put salary first.
You are correct. "...who put salary first" is a necessary part of the description of "those" and so must be written without commas. The first version is incorrect.
Both sentences contain additional errors. There must be a comparative word such as "more" if the word "than" is to be used - and "in first place" is the correct way to use that phrase.