Maybe it would be better to use the usual content URI format so that [ContentUris.withAppendedId] etc can be used. This would then be

JtxContract.JtxICalObject.CONTENT_URI/<id>  =
content://at.techbee.jtx/<JtxContract.JtxICalObject.CONTENT_URI_PATH>/<id>  =
content://at.techbee.jtx/icalobject/<id>

Maybe it would be better to use the usual content URI format so that [ContentUris.withAppendedId] etc can be used. This would then be

JtxContract.JtxICalObject.CONTENT_URI/<id>  =
content://at.techbee.jtx/<JtxContract.JtxICalObject.CONTENT_URI_PATH>/<id>  =
content://at.techbee.jtx/icalobject/<id>

Sure, I'll update the code now.

@rfc2822 , I have added constants for the intent view content uri to the contract. Additionally I have added a convenience function to build the right content uri with the iCalObjectId as last path segment. I created to pull request for sync tools here:
bitfireAT/synctools#110

If you're okay with that, I'll merge the jtx Board code.

The line to call the intent would now be:
./adb shell am start -d "content://at.techbee.jtx/icalobject/2" -W at.techbee.jtx:MainActivity2