Question

Which region of the grasshopper's body is specialized for sensory functions?

Answer 1

None. As with other creatures, the grasshopper's sensory organs are distributed to different parts of its body.

Explanation:

The grasshopper senses touch through organs located in various parts of its body, including antennae and palps on the head, cerci on the abdomen, and receptors on the legs.

Organs for taste are located in the mouth, and those for smell are on the antennae.

The grasshopper hears by means of a tympanal organ situated either at the base of the abdomen (Acrididae) or at the base of each front tibia (Tettigoniidae).

Its sense of vision is in the compound eyes, while change in light intensity is perceived in the simple eyes (or ocelli).
https://www.britannica.com/animal/grasshopper-insect

See also:
https://comparativeanatomybiology.weebly.com/grasshopper-anatomy.html
for some nice graphics and other perspectives on grasshopper anatomy.