I want to apply SNORM texture by using GL_TEXTURE_3D as a target, what will be the fragment shader for the same? Also, what should be the data type of texture data?
RGBA_SNORM you should use
GL_BYTE with four components per texel to fill it.
It is basically the same as normal UNORM textures only that you get a value between
1.0 when sampling.
The signed byte value is mapped -127 -> -1.0 and +127 -> 1.0. -128 is dropped.
Sampler type is sampler3D (Floating-point also covers normalized integer formats).