What is one thing that citations show a reader

A "citation" is the way you tell your readers that certain material in your work came from another source. It also gives your readers the information necessary to find that source again

Giving credit to the original author by citing sources is the only way to use other people's work without plagiarizing.

He would most likely be employed by a gov. agency or homeowner because he has the required skills that have to be known to apply and get hired into those jobs.

You forgot to add the possibilities. we don't know the options from which to choose.