applicationhost.config file path in IIS 7, 7.5, 8, 8.5 and IIS 10?

For the "big" IIS versions since IIS 7, the location is always the same:

 %windir%\System32\inetsrv\config\applicationHost.config

For IIS Express there is one per user, the default location is:

%USERPROFILE%\Documents\IISExpress\config\applicationhost.config

again it's the same for all versions.

You can run multiple instances of IIS Express per user, you would need to specify the location of the applicationhost.config as the command line parameter /config for iisexpress.exe

You can delete one or more site in IIS server 7 or above using the application host config file which resides under the "windows/system32/inetsrv/config" folder.

If you want more detailed information then you can read this blog post Delete or manage one or more IIS websites through application host configuration file