@arnschi Currently there is no such log. Maybe you can just have a look into the calendar from time to time and see whether your events are available and up to date?
unable to sync with owncloud calendar
Davdroid is unable to contact with owncloud calendar.
0_1451112603719_davdroid-debug980229518.txt Check uploaded file for debug info.
As you can see in the logs, the TCP connections have been refused. This is a server or firewall problem and very likely not a problem of DAVdroid. Please contact your administrator, or if you are the administrator, fix the network problems.