Ogat

From Memory Alpha, the free Star Trek reference.

Ogat is a Klingon planet. It is home to a residential training academy for young Klingons studying the way of the warrior. The academy course is difficult, but the teachers are excellent.

In 2370, K'mtar suggested that Alexander Rozhenko should leave his father and attend the academy on Ogat in order to better train for a warrior's life. Worf ultimately refused, and Alexander remained on the USS Enterprise-D a while longer. (TNG: "Firstborn")