I wanted to double-check this Possessive + object

Is this correct for "I know his friend."?

Onun arkadaşını biliyorum.

Could "arkadaşını biliyorum" on it´s own also be "I know your friend."?

Yes, "arkadaşını biliyorum" can mean both "I know your friend" and "I know his/her friend".

The attached prefixes in both cases are different, but end result is the same:

1. I know your friend: arkadaşın-ı (your + accusative) biliyorum

2. I know his/her friend: arkadaşı-nı (his/her + accusative with buffer letter "n") biliyorum.

As far as I know, you can use words like "senin" and "onun" to disambiguate this sentence:

1. I know your friend: Senin arkadaşını biliyorum.

2. I know his/her friend: Onun arkadaşını biliyorum.

Unfortunately, I don´t know which option is more often used in colloquial speech: using "senin/onun" or not using it and relying on context. Perhaps native speakers or more advanced learners can advice here.