Answer:
"The program was written by Sara, who is an expert in her field."
"To whom should I talk to about the report?"
Explanation:
Who is a pronoun that represents the subject of a sentence:
Whom is a pronoun that represents the object of either a verb or a preposition:
By replacing the pronoun with he/she or him/her it is easier to realize its function:
Who/whom took my laptop?
He took my laptop (RIGHT) - him took my laptop (wrong)
So in this case, the correct pronoun to use is who.
Who/whom should I talk to about the issue with my boss?
I should talk to he (wrong) - I should talk to him. (RIGHT)
Here, the correct pronoun to use is whom.