Jack Kirby's the Demon:
The Demon #7, The Demon #14, and The Demon #15
Klarion first appears in the seventh issue of the first run of the Demon. Although we learn a bit about his background and abilities at this point, his rather mischievous intentions are shown in the fourteenth and fifteenth issues.
Grant Morrison's Seven Soldiers
Seven Soldiers: Klarion #1 - From This World To That Which Is To Come
Seven Soldiers: Klarion #2 - Badde
Seven Soldiers: Klarion #3 - The Deviant Ones
Seven Soldiers: Klarion #4 - Burn, Witchboy! Burn!
Each of these comics show most of Klarion's adventure as one of the Seven Soldiers. All four of his issues make sense without reading the rest of the Seven Soldiers series.
Klarion's background is largely expanded on from what was shown during the first run of The Demon. His appearance is also changed to reflect a more magical character. While on his adventure in the "Blue Rafters" he is confronted with the possibility of becoming more than what all the comics have previously made him. Can Klarion be a hero or will he strike out for himself?
Robin #157 - Things That Go Bump in the Night and Robin #158 - Strange Brew
Klarion's familiar Teekl has been separated from Klarion and finds himself in the arms of Batman's sidekick Robin. While trying to care for the cat Robin gets mixed up with a horigal that seems to have escaped from Limbotown. He teams up with Klarion to get rid of the beast and return all the familiars to their owners.
Superman/Batman: Sorcerer Kings
In this story arc, Superman and Batman must stop some magical villains from taking some serious power. In order to do that they will need the help of other mystical characters including Klarion. This version of Klarion is the same as presented in Morrison's Seven Soldiers. It showcases a more heroic side of him but that does not mean he has lost his love for mixing things up.