I would like to know please, which words should be capitalized in this sentence:
The officer won the competition and got to meet the writer of the book.
I am especially interested in the word "officer." This sentence was part of a year 5 dictation. It was a one-off sentence and nowhere before this sentence was there a reference to any "officer."
Thank you

From a grammatical standpoint, there is no need to capitalise the word officer. However, you have touched upon a grey area. On occasion, for etiquette purposes, it is considered polite to capitalise some words, like director, manager, unit, regiment, etc.

I do not condone this, but it is a practice documented in a number of the leading grammar references. There is more on this here at point 2 (business writing).