Not available in single player. Lasombra enemies in single player use Dark Hunter, the only skill granted by this tome.
The Age of RedemptionMod adds a full five abilities to both Redemption single player storyline and Multiplayer. Dark Hunter is not included.
Players cannot choose a Lasombra character in multiplayer without a mod. Lasombra enemies in multiplayer can use Dominate and Potence skills as well as Obtenebration. The Lasombra clan and powers were added to Multiplayer by the Within the Darkness mod, but the powers were still reserved in comparison to the Mind's Eye / tabletop version.