You need to use “work experience” when you want to write about all of the jobs you have had in your career on your C.V.
Work experience is usually used as a heading on your C.V to describe your career. It is a way to show the different jobs that you did.
Here is a sample C.V with work experience as a heading
Work experience is also when you are a student in school and you spend a week or two working for a company just for the experience. You usually don’t get paid for this role.
Work experience can also be used by companies when they are looking for a new employee.
We need someone with 5 years of marketing experience.
Experience is an uncountable noun so there is no need to add an s. Work experiences is incorrect.
Working experience is not incorrect but it is not common in English.
You can use working as an adjective but it is not commonly used with experience. You can use it another way, however.
I have experience of working in the mines.
Working is commonly used as an adjective with the following nouns: man, woman, knowledge
He is a working man.
I have working knowledge of how to operate machinery.
Work experience is a common way to talk about the work that you have done. You do not need to use Working experience in English.