Answer by taking a quote from the following article:

Leonard, the fifth of seven children of Cicero and Getha Leonard, was born in Wilmington, North Carolina. He was named after Ray Charles, his mother's favorite singer. The family moved to Washington, D.C., when he was three, and they settled permanently in Palmer Park, Maryland when he was ten. His father worked as a supermarket night manager and his mother was a nurse.

On December 7, 1989, Leonard defended the title against Roberto Duran, who was the reigning WBC Middleweight Champion. Duran was guaranteed $7.6 million and Leonard's arrangement guaranteed him over $13 million.  For the Duran fight, Leonard cut his entourage from twenty-one to six. Dave Jacobs was one of the people let go, leaving Correa as the sole trainer. Correa was instructed not to spare the whip. "For the first time in a long time, I allowed someone to push me", Leonard said.  The fight took place at the new Mirage Hotel in Las Vegas. Leonard used constant lateral movement and won by a lopsided twelve-round unanimous decision over a listless Duran. The scores were 120-110, 119-109, and 116-111. In a fight that many considered to be very boring, both fighters were booed often by the fans and many left the arena before the decision was announced. Pat Putnam of Sports Illustrated wrote, "Leonard gave them artistic perfection when they wanted heated battle, and they booed lustily. Most fight fans would not spend a dime to watch Van Gogh paint Sunflowers, but they would fill Yankee Stadium to see him cut off his ear." Although Leonard dominated the fight, he suffered several cuts. His lower lip was cut from a headbutt in the fourth round, his left eye was cut in the eleventh round, and his right eye was cut in the twelfth round. The cuts required a total of 60 stitches.  In January 1990, Leonard relinquished the WBC Super Middleweight Championship, saying that he was unsure whether he would fight again. When Leonard decided to continue his career, he offered Hagler a rematch, but Hagler decided to stay retired. He then offered Hearns a third fight, but Hearns said he could no longer make the weight and moved up to the light heavyweight division.

How many knockouts did Leonard have in this fight?
The scores were 120-110, 119-109, and 116-111.