I explained him the problem better but actually he couldn't even help.
But I can copy here my explanation that I have written in my PM.
So I have a wall object that has 4 different textures. As this pictures shows: https://imgur.com/CSJBkSU ( Texture names: la_carp3, la_carp4, la_carp5, la_carp6 ) I checked them with shader_tex_names resource from MTA Wiki. But I'd have to get the name of the texture that I click on. For example, I click on the right side of the wall object then the function gives as result: la_carp3.