"Το κορίτσι του του διαβάζει ένα βιβλίο."
You don't need the accent on the second του because it's clear that one ιis for "το κορίτσι του and the other one is for **του διαβάζει..."
But it's not uncommon to use it.
There have been a few explantatios on this page...Please read the other comments. So, it's
Yes, exactly! It caught me out and I reported it when I shouldn't have done. It shouldn't give this as an option in the hints if it is a wrong translation though, that needs to be fixed.
Look at the top of this page. There you'll find the correct Duolingo sentence.
"His girlfriend reads a book."
If you read "The girl reads him a book." in the comments it does not mean it is the correct sentence. But most of the comments do not say that. There is no "him" in the correct sentence.
When you have a translation to write you should use the Drop Down hints. That means you pass your cursor over the words and it will show you what the correct translation is. If there are a few translations only use the top one.
That way you will always find the right translation without guessing and you'll learn correct Greek.
I wrote "The girl is reading him a book". Why is this not acceptable?
Το κορίτσι του means "his girl" or "his girlfriend". It does not mean "reads him" that would be..."Το κορίτσι τού ...."
You see "το κορίτσι του" shows 'του' without accent so it means "his girl" if we want to say "The girl reads him..." we need to show that "τού" is separate and for that, we use the accent.
Now, to avoid all this complex explanation so early in the course you could have just used the Drop Down hints which would have shown you the precise translation.
There is no accent on "του" because the sentence being taught here does not require an accent since the meaning is "His girlfriend reads a book."
There are several comments emphasizing the difference between:
"HIS girlfriend/girl reads a book."
"The girl reads a book TO HIM."/"The girl reads HIM a book."
Without the accent, it means "HIS".
With the accent, it means "HIM/TO HIM".
Here it DOES NOT NEED the accent.
Please read the comments above where this is explained a few times.
Please read the comment above yours. There it explains why IN GREEK it means....his girlfriend.
If you cannot see the other comments because you are using the app...don't ....get the web course on your phone or whatever you are using.
TIPS TO MAKE LEARNING EASIER + HOW TO REPORT A PROBLEM
And check out the Greek Forum here with more links.