From WoWWiki

The Hall of the Damned is located deep within Scholomance. It is accessed from the Headmaster's Study via the eastern doorway on the upper level. This is where the evil Doctor Theolen Krastinov can be found, amid a few pestilent ghouls.

Subzones of Scholomance
Barov Family Vault • Chamber of Summoning • The Coven • The Great Ossuary • Hall of Secrets • Hall of the Damned • Headmaster's Study • The Laboratory • The Reliquary • The Shadow Vault • The Viewing Room • Vault of the Ravenian