A Triple-Double is when your player gets more than 10 points, 10 assists, and 10 rebounds/steals/or blocks. To me the three that are easier to get are 10 points, 10 assists, and 10 rebounds.
On the "Main Menu">"Game Modes">"Be A Pro". Pick the Celtics and play as Kevin Garnett(Power Forward or PF). He is by far one of the best players in the game. Now try to get 10 points, 10 assists, and 10 rebounds. Set the difficulty to Rookie to make the game easier and play against Angola, they are one of the FIBA teams. They are the worst team in the game. You should easily get a Triple-Double. If you think you will have troulbe getting a Triple-Double set the Quarter Length to either 10 or 12 Minutes.