I question about vertex normals

Hi to all

A simple (maybe) question.
How the exporter manage vertex normals ?

For example thoughts to a cube.
The vertex (1,1,1) is common to three faces with normals (1,0,0) (0,1,0) and (0,0,1). Which is the normal in this vertex ?

Maybe i'm wrong, and the exporter generate three vertex in the coordinate (1,1,1) one with normal (1,0,0) one with normal (0,1,0) ecc...

I made this question because I try to write a simple shader with TSE, but when I work with normals something go wrong.
Normals vectors passed to shader seem wrong.
I don't know if something don't work with normals in the exporter or in Blender (or in me).

Someone know about it ?

Thanks.