A 15-year-old Brooklyn high schooler was asked if he was in a gang before he was gunned down Wednesday, witnesses told police.

Unique Smith, a student at Brooklyn Laboratory Charter Schools, was sitting on a bench near the campus around 1:40 p.m. when two masked men walked up and asked about his gang affiliation, law enforcement sources told The Post.

Police said Smith got into a fight with his assailants and was shot once with a 9mm handgun before the gunman ran off.

Smith was later pronounced dead at New York/Presbyterian Methodist Hospital.

Two witnesses to the fatal shooting told cops that the beef started when the bandits demanded to know if Smith was in a gang.

Police said there was no indication that Smith was a gang member.

The teen’s neighbor Mary Beloti agreed.

“Definitely not,” she said Thursday.

“I can’t wrap my head around it, I really can’t,” said Beloti, 64. “He’s a wonderful young man. Very respectable young man. He went to school, played his music, played his video games, never bothered anybody.

However, Beloti said locals did worry about Smith’s new batch of pals.

“He was not in trouble,” she said. “I think it was the company he kept. We were all very concerned about these boys he hung around.

“These new boys,” she added. “Not his friends, but these new boys.”

The slain teen’s grandfather, Kenneth Davis, told The Post Wednesday that the family was “falling apart” after learning of his senseless death.

Davis offered a $5,000 reward for the capture of the shooter.

“He’s a terrific young man,” he said of his grandson. “He helps around the house. He’s energetic. He’s just an average 15-year-old. It’s sad.”