It depends in part on the reaction to the increase of thrust.
In the very short term, the aircraft accelerates. That means that, in the frame of reference of the aircraft, the "balancing force" is an inertial force at the centre of mass.
As the aircraft's speed increases, the drag increases, and the balancing force is the increase in drag at the centre of drag.
Alternatively, if the aircraft maintains the same speed and climbs, the balancing force is a greater aftward component of weight, at the centre of mass.
So both the centre of mass and the centre of drag ("drag line") may be relevant.