Ziska achieved his first IM Norm in 2008 and won the Faroese Chess Championship in 2011 and 2015. He qualified for the Chess World Cup 2017 after a successful run at the European Individual Chess Championship 2016 in Gjakova, Kosovo. It was in this tournament that he achieved his second and third GM norms, securing his Grandmaster title.
He played for Faroe Islands in the Chess Olympiad, an international team chess tournament, on six occasions between 2004 and 2018. He also represented the Faroe Islands in the European Chess Team Championship on few occasions.