Hi @RealRancor and thanks for your help!
I made these changes:
Redirect 301 /.well-known/carddav /owncloud/remote.php/dav
Redirect 301 /.well-known/caldav /owncloud/remote.php/dav
And now if I point my browser to https://example.com/.well-known/carddav or https://example.com/.well-known/caldav
it ask me owncloud username and password but if I set Davdroid to https://example.com/ it tell me again “Couldn’t find CalDAV or CardDAV service.”
I’ve try also: https://example.com/owncloud/remote.php/dav/principals/username with the same result.
I’ve read your tutorial, where I’m wrong? 
many thanks again!