The server root is a directory under which the Apache executable (httpd) tries to find files show name is indicated with relative paths (such as for example conf/, logs/, or those indicated with Include and LoadModule directives.
The location of the server root is determined in the following order:
The value of the command line option -C together with the ServerRoot directive.
The value of the command line option -d
The current working directory
A registry entry (apparently on Windows?) with a binary installation
The server root as compiled into the server (by default /apache).
As there is always a current working directory, I am not sure how the last two options can ever be considered.