Questions & Answers about Mój brat i mój kolega dobrze się znają.
Yes, you can.
- Mój brat i mój kolega dobrze się znają. – My brother and my friend/colleague know each other well.
- Mój brat i kolega dobrze się znają. – very natural in speech and writing.
When you omit the second mój, it is usually understood that kolega is also your colleague/friend, but it can be slightly more ambiguous from context. Repeating mój makes it 100% clear that both are “mine” and can sound a bit more emphatic or careful.
Polish separates “know” into different verbs:
- znać – to know a person, a place, a thing (to be familiar with it)
- znać kogoś – to know someone
- wiedzieć – to know a fact
- wiem, że... – I know that...
In this sentence we are talking about people being familiar with each other, so we must use znać (się), not wiedzieć.
Mój brat i mój kolega dobrze się znają.
= My brother and my friend know each other well.