In January 2003 Kokslien was on the line-up for the B World Cup for the first time, where he was nineteenth straight away. At the junior world championship of the same year, he placed twelfth in the Gundersen method . After showing consistent results in the B World Cup in 2003 and 2004 and becoming Junior World Champion with the team, he was nominated for the first time for the Nordic Combined World Cup in February 2005 . Here, too, he was able to collect points on his second individual assignment. Nevertheless, the Norwegian Association has not used him in the A World Cup for more than two years, but Kokslien achieved three podium finishes in the B World Cup, including one victory. He was nominated again for the World Cup at the beginning of the 2007/08 season , but at the beginning of the season he was no longer able to score points, so he initially relegated to the B World Cup. Only towards the end of the season did Kokslien return to the highest competition class and, among other things, was 13th at the season finale in Oslo .
In the 2008/09 season Kokslien came in seventh at the World Cup in Ramsau for the first time among the top ten. At the Nordic World Ski Championships 2009 in Liberec , he won the bronze medal with the team in the team competition. A short time later, on March 15, 2009, he achieved his first podium finish in third at the season finale in Vikersund . He finished the 2008/09 season in 21st place in the overall World Cup ranking. At his first Olympic Winter Games in Vancouver in 2010 , Kokslien reached 32nd place in the individual on the normal hill and 39th in the individual on the large hill.
At the beginning of his career, Kokslien had also competed in cross-country skiing races and had placed himself well there. With growing success in Nordic Combined, however, he no longer took part in cross-country competitions.
On March 10, 2018, Kokslien ended his career on his 33rd birthday with the competition in Oslo.
Norway
Oberstdorf
Almaty
Ramsau
Chaux-Neuve
Val di Fiemme
Kuusamo
Liberec
Steamboat Springs
