From WoWWiki

The Headmaster's Study is located deep within Scholomance. It is accessed from the Viewing Room via the eastern doorway. The study is surrounded by six antechambers over two levels accessed from the southern, eastern, and northern walls. Each of these rooms has one mini-boss, which must all be killed for the school's headmaster, Darkmaster Gandling to appear in his study. This is Scholomance's final boss.

The antechambers and their respective minibosses are as follows:

• Upper level, northern chamber - Hall of Secrets - Lorekeeper Polkelt
• Upper level, eastern chamber - Hall of the Damned - Doctor Theolen Krastinov
• Upper level, southern chamber - The Coven - Instructor Malicia

• Lower level, northern chamber - The Shadow Vault - Lady Illucia Barov
• Lower level, eastern chamber - Barov Family Vault - Lord Alexei Barov
• Lower level, southern chamber - Vault of the Ravenian - The Ravenian

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