The big thing that Duclair needs to fix in his game is his play without the puck, particularly in the offensive zone. A lot of the time you'll just see him kind of float around and hope the puck comes back his way, but he doesn't necessarily take himself to high percentage areas or places that he can easily pounce on a rebound. He just gets sort of aimless at times.
That's the sort of thing he really needs to learn from NHL coaches, though. His skill level is too high for juniors, so he can continue those bad habits and still be rewarded for it. That's also why he has more goals playing with Domi and Reinhart than he did playing with Rick Nash and Martin St. Louis.
I'm not sure how that was even ruled a goal on the ice to begin with.