My head exploded the first time I saw this, but it's actually the same word order we've been using all along, just getting more complex. If we think of "onun hakkında" ("about him/her") as just another modifyer /adjective-phrase, it may seem more familiar...
büyükbir kitap = This is a big book
onun hakkındabir kitap = This is a book about him
And if you're struggling with "onun hakkında" (about him/her) you could try thinking of this as "on the topic of him/her" to remember the structure: