Questions & Answers about Koleginica koja radi sa mnom danas nije u kancelariji.
Koleginica means female colleague, while kolega usually means male colleague (and in some contexts can also be used more generally for colleague).
In this sentence, koleginica tells you the person being talked about is a woman.
- kolega = a male colleague / colleague
- koleginica = a female colleague
Koja means who in the sense of a relative pronoun, connecting koleginica with extra information about her:
- Koleginica = the colleague
- koja radi sa mnom = who works with me
So koja refers back to koleginica.
It changes form depending on gender, number, and case. Here it is koja because it refers to koleginica, which is feminine singular.
Compare:
- čovek koji radi... = the man who works...
- žena koja radi... = the woman who works...
Serbian word order is fairly flexible, but this sentence uses a very natural structure: