Here is the most likely identification and a guide to the topic. There is a famous Yugoslav film from 1978 titled "Ko zorijo jagode" directed by Rajko Ranfl . It is a coming-of-age drama set in a small Slovenian town.

Based on the spelling and context, "Ko zorijo jagode" is a Slovenian phrase meaning (or "When the Strawberries Are Ripe"). The year 1978 and the abbreviation "ok ru" likely point to a specific film, TV production, or book from that era.