He occupies the "bumper" position and thus replaces Tanner Pearson.
"Alex Newhook is practicing on the first power play for the Montreal Canadiens instead of Tanner Pearson. This means that his return to the game is approaching." - Renaud Lavoie, TVA Sports
He is the true replacement for Sean Monahan on the five-man attack. See also the new complete units, according to Anthony Martineau:
PP1: Caufield-Suzuki-Newhook-Matheson-Slafkovsky
PP2: Anderson-Gignac-Ylonen-Pearson-Xhekaj
It will be interesting to see Newhook back, especially with such significant responsibilities. More details to follow.