dpkg -L expect will list the
/var/lib/dpkg/info/expect.list file for the package which lists full path of the each of the packages files. You may want to pipe it to
less so you can read it.
man hier should give you a description of the file system hierarchy used by Debian. The maintainers tend to be quite religious about following it and will often create symlinks to directories to allow programs that don't follow it to work within their structure.
Documentation goes in
/usr/share/doc/<package-name>, so expects documentation will be found in
/usr/share/doc/expect. There may be multiple
example subdirectories below that, along with other directories which may contain runnable code. man pages go elsewhere, but can be found with the command
man -k expect.
For other packages just replace
expect in the above commands with the package name.