It means exactly what it says...to write about what you know. If you know about something than you'll have more to say and have an opinion. If you don't know about a subject...there's less to say.
The answer is WHO because WHO is used when referring to a person.
Hope this helps!!!!
The answer is <span>the </span>speaker<span> needs someone to whom she </span>can<span> pose her questions.</span>
