Is there really anything wrong with 'Whose books have you?'. It's perhaps a bit archaic or posh but could it work?
We've recently started accepting phrases like that, since they are apparently quite common in the UK. Feel free to report if it is rejected anywhere!
I have mistaken broeken and boeken so many times! And I totally DID expect "whose pants are you wearing" from Duolingo XD
I swear she says "hep". I don't know that word, but it definitely didn't sound like "heb".
At the end of a word the letter b is sounds like a p, but otherwise it sounds like a b in english
Can that refer to authors of said books?
Couldn't it be "Which books do you have?" instead?
That would be 'Welke boeken heb je/jij?'
shouldn't it be "hebt"?
You drop the t when jij (or je) comes after the verb. There's a number of comments about this on similiar challenges, if you look around.