"I worked in a chemists" vs "I worked in a chemist's" vs "I worked in a chemist"? [duplicate]
I worked in a chemist
Er, no: that would be rather uncomfortable for both of you!
I worked in a chemists
Chemists is a plural noun, so a chemists can't be correct.
I worked in a chemist's
This is an example of ellipsis: "I worked in a chemist's [shop]". Using the possessive is entirely correct.
I worked for chemists during my first two years of university.
This is correct: chemists is a plural noun, indicating that you had more than one employer/mentor.
Store names & possessive deals with people's names, not shop types.