What is the net force acting on a falling object when it reaches terminal velocity?

Net force = 0

Explanation:

An object reaches its terminal velocity when the air resistance or drag force becomes equal to the weight of falling object. In this condition, the object is moving with constant speed.

And we know that acceleration, a = rate of change of velocity

If v = constant, then acceleration of an object is 0. Net force acting on an object is given by the product of its mass and acceleration as per Newton's second law i.e.

So,        

Hence, net force acting on a falling object when it reaches terminal velocity is zero.

if they have a finite resultant