Xcode: View Console History After Cleared?

Xcode console output is logged in the system log. You can search the system log from the console with grep:

# view last 2000 lines of the system log
sudo tail -n2000 /private/var/log/system.log

# search system log for YourApp
sudo grep YourApp /private/var/log/system.log

# watch the system log as it's being written and filter for YourApp
sudo tail -f /private/var/log/system.log | grep YourApp

Xcode 11:

In the Navigator, press the "Report navigator" button (the speech bubble), then click on your previous run sessions. You can see all your previous console logs.