From fossil help pull:

    The URL of the remote server is specified on the command
line. If no URL is specified then the URL used by the most
recent "pull", "push", or "sync" command is used. 

This also affects auto-sync. But there is no way to see the recorded URL without resorting to sqlite access...

    sqlite> select value from config where name = 'last-sync-url';

DRH on mailing list:

    Why not just add a line of output to "info"?

    Be careful, though.  The query shown by Kees is not sufficient.  The  
URL stored in the database might contain a username and password.  The  
"sync" command is careful to strip those off before displaying the  
URL.  If added to the "info" command, it should likewise hide at least  
the password.

DRH also suggested reasons to have a separate command: so that you can change or
remove the default remote-host

     fossil remote-url     # Display the currently saved URL (suppressing the password, of course)

     fossil remote-url URL # Change the currently saved URL
without doing a sync, push, or pull

     fossil remote-url off # Remove the currently saved URL

Stephan asked: would it make sense to tie it in as a new setting? e.g.

    fossil set remote-url       # show

    fossil set remote-url URL   # set

    fossil unset remote-url     # remove