There are different NBA players to watch in order to learn different skills.
If you want to study the game of passing, then watch Ricky Rubio. Rubio is a guy that never shot well or had any athleticism. He made his money by studying the game and making elite passes to his teammates.
If you want to study the game of shooting, then watch guys like Steph Curry, Damian Lilliard, and Kyrie Irving. They are both fundamental and creative. Study their decision making and the type of shots they like to take.
If you want to study the game of catch and shooting, then watch Duncan Robinson. This is a man that played D-3 basketball and worked his way into the NBA. Study the way he moves without the ball and gets himself open for shots.
If you want to study the 3 and D game, then watch players like Klay Thompson and PJ Tucker. These guys are elite scorers, but also shut it down on the defensive side. These guys are very essential to their team, and you could make it far in basketball if you can play like them.
If you want to study the post game, then watch players like Nikola Jokić and Karl-Anthony Towns. Study their footwork and the way they use their bodies to position themselves for easy shots.
If you want to study the game of rebounding and defending big, then study guys like Mason Plumlee and Jared Allen. These guys define toughness and hustle, something that any less skilled player can work on in order to get minutes on their team.