4 Answers

Good sensible leather lace ups. With a steel toe cap if you are required to defend yourself.WBMS.

It depends in which country you live and what kind of office job you have. In India, bare feet or thongs are fine depending on the type of job. In Sri Lanka, it is the same. In Western countries they like everyone to have a nice pair of shiny shoes.

flat or small heeled, and closed in, not sandals, high heels or gym shoes (runners), footwear even in an office often has to meet with OH&S standards now

OFFICE ATTIRE! I can tell you what is NOT appropriate:
Athletic shoes
Flip Flops of sandals that have a separated big toe
Open toed shoes
House or Bedroom slippers
Excessively high heels

Good answers from Umbriel and lambshank