Witnessed by the those living in heaven; the angels, because the record of the righteous is an honorable pure book.
الْمُقَرَّبُونَ (those brought near to Allah): The angels in the highness because everything in this book is about obedience to Allah (swt). Since angels love obedience because they are honoured slaves who do not disobey Allah (swt) whatever He (swt) commands them and they do what they are ordered to do. However, this verse is not mentioned concerning the record of the wicked, because it is a Book of evil, guilts and badness, so how the angels will witness it!!
When the speaking was about the Book of the wicked, the context moves directly from (It is [their destination recorded in] a register inscribed (9) to (Woe, that Day, to the deniers, (10)), because their book is a misfortune and disgrace upon them, they are ashamed of it, wishing not to see it. While, the Book of the righteous is witnessed by those near to Allah (swt) which indicates the harmony of the universe with obeying Allah (swt) and showing Him (swt) submissiveness and enslavement.