I see the output in the console window, like this:
QT_LOGGING_RULES="*.debug=true" krdc
No protocol specified
qt.qpa.screen: EDID data for output "eDP1": identifier 'B173HAN01.0', manufacturer 'B173HAN01.0',model '', serial '', physical size: 380.00x210.00
qt.qpa.screen: Output HDMI1 is not connected
qt.qpa.screen: Output VIRTUAL1 is not connected
qt.qpa.screen: adding QXcbScreen(0x555e5681ef20, name="eDP1", geometry=1920x1080+0+0, availableGeometry=1920x1044+0+0, devicePixelRatio=1.0, logicalDpi=QPair(96.0,96.3), physicalSize=380.0x210.0mm, screenNumber=0, virtualSize=1920x1080 (1920.0x1080.0mm), orientation=Qt::ScreenOrientation(LandscapeOrientation), depth=24, refreshRate=60.0, root=167, windowManagerName="KWin") (Primary: true )
qt.qpa.screen: primary output is "eDP1"
qt.qpa.input: Plugin build with support for XInput 2 version up to 2.2
qt.qpa.input: Using XInput version 2.2
qt.qpa.input.devices: input device Virtual core XTEST pointer ID 4
qt.qpa.input.devices: has 10 buttons
qt.qpa.input.devices: has valuator "Rel X" recognized? true
qt.qpa.input.devices: has valuator "Rel Y" recognized? true
qt.qpa.input.devices: it's a scrolling device
qt.qpa.input.devices: input device PixArt HP USB Optical Mouse ID 10
...
But I’m using Tumbleweed and have additionally the debug packages installed (krdc-debuginfo-18.04.1-1.1.x86_64)
Hendrik