This is the 95th most frequent Slovenian word.
katerem
"Katerem" is the locative or instrumental singular form of "kateri," meaning "which" or "in which."
The word 'katerem' here is used as a relative pronoun in the locative case referring back to the subject 'movie'.
To je film, o katerem sva se že pogovarjala.
This is the movie we already talked about.
The word 'katero' here is functioning as a question word (interrogative pronoun) in accusative case for the direct object 'restaurant'.
Katero restavracijo nam boš priporočil?
Which restaurant will you recommend to us?
The word 'katerem' here is a question word (interrogative pronoun) in locative case referring to the location 'city'.