I have recently updated Xcode to version 10, and now my console displays:
MyApp[1618:133310] [AXMediaCommon] Unable to look up screen scale
MyApp[1618:133310
This won't answer your original question, but it might relieve your eyes. A caveat to this answer however is that it disables all NSLog statements.
Do the following to suppress - all NSLog statements including - the warning: Unable to look up screen scale:
In Xcode, go to Product - Scheme - Edit Scheme, select 'Run' on the left side ...
... and add OS_ACTIVITY_MODE with value "disable" in the Environment variables section.