The mok'bara is a Klingon form of martial arts, similar to Tai Chi.
Curzon Dax was a lifelong student of the mok'bara. (DS9 novel: Avatar)
Worf's mother, Kaasin, had also been a mok'bara master, and taught classes while on Khitomer. (TLE novel: The Art of the Impossible)
As an adult, Worf became a master of the mok'bara, and led sessions aboard the USS Enterprise-D. One of his best students was Ensign T'Mor. (TNG - Perchance to Dream comic: "By a Sleep to Say We End")
Deanna Troi was also a student of Worf's, and reached the rank of chu'wI'Hey, or advanced novice. (TNG - Slings and Arrows eBook: The Insolence of Office)
In 2373, Worf began to teach Alexander Rozhenko mok'bara as a way to control Alexander's anger. (DS9 - Day of Honor novel: Honor Bound)
After Worf returned to the USS Enterprise-E in 2379, he resumed teaching mok'bara classes. (TNG novel: Q & A) He provided a private session to Lieutenant Jasminder Choudhury after she took interest in him. ST