one of my friends' friends or one of my friends' friend
I have many friends, and one of them has a friend.

I wasn't sure whether the sentence I said was correct "one of my friends' friend"

What would a native English speaker say naturally?

Question

one of my friends' friends or one of my friends' friend
I have many friends, and one of them has a friend.

I wasn't sure whether the sentence I said was correct "one of my friends' friend"

What would a native English speaker say naturally?

Answer

The expression "one of the ..." or "one of my ..." etc always takes a noun in the plural -- One of the best cars in the world ...

When you write "One of my friends' friends" the first word "friends'" is a possessive modifying the head noun, which is the second word "friends". The head noun must be plural after "One of the ...".

Answer

I assume that your friend has more than one friend, too, so the first answer ("one of my friends' friends") is correct.