I would think the case with 2. person plural works as well (Hvordan skriver I jeres bog?)
Why is it not "sin" book? I thought sin and sit are reflexive?
i need to know this as well. or are both correct?
what does din mean?
By bog not bøg?
'en bog' means 'a book', 'bøger' on the other hand means 'books'
Why "hvordan" is true, and "hvor" is false?
Because the translation for „how“ is mostly „hvordan“.
Hvor translates (in most cases) to „where“, unless you want to know how big/small/cold/far away/... something is. :)