Best I can tell, you can find Time Machine logs with Console.app using the query "process:backupd category:TMLogError" or from the command line:
log show --predicate "'process == "backupd" AND category == "TMLogError"'
However, this doesn't return nearly the amount of useful information that you could get from the syslog command in previous OS versions. In fact, so far it's been next to useless helping me debug my TM problems. Maybe there are better search criteria that I should be using. If anyone knows, please post.
Also, Console.app only seems to let me view live events. If it wasn't open when an error occurred, I can't search for it. I have to use the log command in Terminal. Is there some documentation for Console.app that I'm not finding? If you view Console Help from within the app itself, those docs haven't been updated for Sierra.