Weah put in a solid shift, but it seems clear that he's still very much in the adjustment phase at Juventus.
The American never really took any early opportunities to beat a man off the dribble, instead generally taking the safer options. The willingness to go at players comes with confidence, and Weah will need to build his in his new surroundings at Juve.
He's clearly on the right track, though, as he looked like an entirely different player as the game wore on. He had a dangerous second half, creating two chances and forcing a good save as Juve chased a goal. He likely deserved a goal or assist given his efforts on the day.
One thing to watch, though, is Weah's tendency to drift inside. He played centrally for large stretches of the match, moving into the middle of the field to receive the ball. That may have been a function of Massimiliano Allegri's tactics for the day, but it's also something to watch from a player that is generally known as a speedster able to get to the end line.
As for Weston McKennie, it appears that, at the moment, he's a backup. Juve started with Rabiot, Manuel Locatelli and Nicolo Fagioli in midfield, with Paul Pogba coming off the bench in the second half. McKennie has spelled Weah at wingback, definitely not his natural position, but he faces a real fight to get into that midfield.