Janičenoks first gained attention as a high scoring teenager at the 1999 FIBA Europe Under-16 Championship. He was the second leading overall scorer at the tournament, averaging 23.5 points per game and was named to All-Tournament Team. Shortly thereafter, he started his career in Latvian Basketball League with Brocēni. In 2001, after finishing high-school in Latvia he received multiple offers from NCAA D1 schools, choosing George Washington as the place where he will play. However, NCAA ruled him ineligible due to fact that he had played with Brocēni in NEBL which was considered as pro league although he didn't get paid. After one month in USA, he returned to Latvia in September and joined newly founded BK Skonto, which was a successor to Brocēni. In 2003, he went to play abroad, joining Belgian side Liege Euphony. In the following season, Janičenoks moved to German Bundesliga team Telekom Baskets. In 2005, Kristaps signed with Italian top division team Upea Capo d'Orlando. His first season in Italy was successful and he moved to Climamio Bologna, who at the time was one of the strongest teams in Europe. At the beginning of 2006–2007 season Kristaps debuted in Euroleague. Later in the season he was loaned from Bologna to Teramo Basket. Janičenoks averaged 12.4 points on 40.1% three-point shooting for Teramo. After one season Janičenoks returned to Bologna, but it wasn't a year that he would have expected. After a 2007–08 season in which he averaged a full season career low of 23 minutes and 8.4 points per game with Upim Bologna of the Italian League, he spent 2008–09 with Reyer Venezia Mestre of the Italian second-tier LegADue. He returned to form in 2008–09 as one of the second-tier league's top scorers, averaging 18.1 points per game over 19 games. In 2010, after several years abroad, he moved back to Latvia and signed with VEF Rīga. On December 7, 2010, Janičenoks scored 32 points in a win over Cajasol Sevilla helping VEF Riga to get its first ever victory in Eurocup competition. As captain of the team Kristaps led VEF to its first ever LBL championship and also BBL finals appearance. In 2012, Janičenoks helped VEF to repeat as LBL winners while also leading team to its first Eurocup Last 16 appearance. His most successful season with VEF Riga was 2012–13 campaign, when he was key part of team that made noise in entire Europe with some big wins, however, team didn't reach its full potential. At the end of the season VEF won its third straight LBL title. On November 22, 2014, Janičenoks signed with BK Ventspils.
Janičenoks is a member of the Latvia national basketball team. He has participated at EuroBasket 2005, EuroBasket 2007, EuroBasket 2009 and EuroBasket 2013. At qualification for EuroBasket 2009, he hit a buzzer-beating three-pointer to beat Macedonia in the first group game to help lead the team to eventual qualification for the championships. He also hit game-winning shot at EuroBasket 2013 against Montenegro.
