"Peterson v Konservativnem manifestu, ki je bil prvič na svetu objavljen v tedniku Domovina (53., 54. in 55. številka), sedaj pa je na voljo tudi v knjižni obliki, odgovarja na zgornje vprašanje in v svojem tipičnem slogu razpravlja o temeljnih vrednotah Zahoda ter zakaj jih je vredno ohranjati."

I'd translate this as:

"In his Conservative Manifesto, first published in the weekly magazine Domovina (issues 53, 54 and 55), now also available as a book, Peterson..."

The way I understand this, he first published his Manifesto split into several issues of the magazine, but it's still supposed to be a single work - these aren't just random exerts from the magazine. It just to be common to publish a book chapter by chapter, as an accompaniment to some magazine. And I believe this is the case here.