Refer to figure.
This question can be solved by applying Bernoulli's Principle to the air flowing accross the aerofoil in the question. Bernoulli's Principle states that the total pressure remains constant for an incompressible fluid (like air at low Mach numbers) along a streamline, where total pressure is the sum of static and dynamic pressure;

Static Pressure + Dynamic Pressure = Total Pressure (Constant)

Any time the static pressure increases, the dynamic pressure (airspeed) must decrease, and vice versa. As air can not flow accross streamlines, when streamlines move closer together the air flowing within them must speed up to pass through the narrowing gap. The dynamic pressure increases, so the static pressure decreases.

The question describes a positively cambered aerofoil at a positive Angle of Attack (AoA) as in the figure. Let's consider each option:

On the leading edge of the wing. - Near to the leading edge we see a stagnation point where the air has been brought to a complete stop. The dynamic pressure is zero, and the static pressure is maximum, so this is not correct.

Slightly above the wing, where the airflow is fastest (correct answer). - Streamlines are closest together in this area. The airflow is accelerated to its fastest speed - and so the static pressure must decrease to its minimum value, making this the correct answer.

Below the wing, where dynamic pressure is lowest. - Dynamic pressure below the wing is not at it's lowest value, as discussed. Anywhere that dynamic pressure is low, we expect an increased static pressure so this is not correct.

Slightly behind the leading edge, on the upper surface of the wing. - There are two reasons this is not correct: Firstly, only slightly behind the leading edge the air has not yet accelerated to its maximum dynamic pressure, as in the correct answer. Secondly, on the surface of the wing, air is significantly affected by friction in the boundary layer and so is slowed down much more than air slightly above the surface.