Following the links from Sonarr’s show page for The Dunk King:
Trackt shows 1 season: https://trakt.tv/shows/the-dunk-king
TVDB shows 1 season: http://www.thetvdb.com/?tab=series&id=311670
IMDB shows 2 seasons: http://www.imdb.com/title/tt5731602/
TV Maze shows 2 seasons: http://www.tvmaze.com/shows/14777/the-dunk-king
BUT, Sonarr only shows 1 season on the show page, so it never tries to search for season 2.