This is the 13510th most frequent Polish word.
pewniaki
"Pewniaki" refers to things or people that are certain, guaranteed, or sure bets.
Here, 'pewniaków' refers to exam questions or topics deemed certain to appear on the test.
Znam kilka pewniaków na jutrzejszy egzamin.
I know a few sure things for tomorrow's exam.
In this instance, 'pewniak' refers to a movie that is a certain great choice for entertainment.
Ten film to prawdziwy pewniak na wieczór.
This movie is a true sure choice for the evening.
Here, 'pewniak' is used to describe a horse seen as a certain winner in a race.