This is the 116th most frequent Croatian word.
kojih
"Kojih" means "which" or "of which" in English, used as a genitive plural form.
The word 'kojima' here is the instrumental plural form of 'koji', referring to 'books' (knjige) and stands for 'about which' in English.
Ovo su knjige o kojima sam ti pričao.
These are the books I told you about.
The word 'kojima' here is the instrumental plural form of 'koji', linked to 'ljudi' (people) and establishes the connection 'with whom' in English.
Ljudi s kojima radim su vrlo ljubazni.
The people I work with are very kind.
The word 'kojima' here is the locative plural form of 'koji', relating to 'days' (dana) and expresses 'during which' in English.