[2] Karničnik played for the youth teams of Slovenian club Dravograd before moving to the Styrian League side Radlje ob Dravi in 2013 to start his senior career.

[8] After only five games played in the first part of the 2022–23 season,[2] he returned to Slovenia in December 2022 and joined Celje on a one-year loan.

[2] Karničnik made his debut for the Slovenia national team on 8 October 2021 in a World Cup qualifier against Malta.

[11] In June 2024, he was called up to the squad for UEFA Euro 2024 by Slovenian coach Matjaž Kek.

[12] He played the full 90 minutes in all four Slovenia matches at the tournament,[13] and also scored in the 1–1 group stage draw against Serbia.