Answer
The y components of these two electric field vectors add.
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.
The y component of the electric field due to the $-q$ charge on the left points in the negative y direction. The y component of the electric field due to the $-q$ charge on the right also points in the negative y direction.
Since these two y components point in the same direction, they add.
Therefore, the y components of these two electric field vectors add.
