Książnik [ˈkɕɔ̃ʐnik] is a village in the administrative district of Gmina Miłakowo, within Ostróda County, Warmian-Masurian Voivodeship, in northern Poland. It lies approximately 4 kilometres (2 mi) south of Miłakowo, 31 km (19 mi) north of Ostróda, and 35 km (22 mi) north-west of the regional capital Olsztyn.