typedef struct
{
void LeftClick();
} AwakeGUI_WindowElement;

function odd();
{
}

AwakeGUI_WindowElement Element;

Element.LeftClick = odd;
Element.LeftClick(); // ERROR

?

Waaaaaaaaaaaaah!

This is no valid C code. In C you can store function pointers in struct elements, but you can't call a struct element.

I know I can't treat a void like a function, I posted to get to know how I can archive something similar.

Just as you did, only without the struct.

void LeftClick();
LeftClick = odd;
LeftClick();