Answer
Since the two electric field vectors do not point in the same direction, the magnitude of the net electric field at P is not equal to the sum of the magnitudes of the two field vectors.
The magnitude of the net electric field at P is less than 2E.
Work Step by Step
We can find write the general equation for the magnitude of an electric field:
$E = \frac{\vert q \vert}{4\pi ~\epsilon_0~r^2}$
Note that a magnetic field points toward a negative charge.
Since each charge is $-q$, which is a negative charge, each electric field is directed toward the charge producing it.
When we add electric field vectors, we must add the electric field vectors as a vector sum. Since the two electric field vectors do not point in the same direction, the magnitude of the net electric field at P is not equal to the sum of the magnitudes of the two field vectors.
The magnitude of the net electric field at P is less than 2E.
