For reporting bugs in KDE at bugzilla.opensuse.org, it is helpful to know which packages are installed. Some have only the official openSUSE packages installed and others use packages from KDE repositories.
More information: Debugging KDE
Before you report bugs
Not all bugs you find belong into openSUSE's bugzilla. So before you report anything to bugzilla.opensuse.org, please consider the following:
Report at bugzilla.opensuse.org or bugs.kde.org?
With their limited resources the openSUSE team has to focus on openSUSE-specific bugs/features. Further, they cannot be experts for every single application, so the maintainer of an application at bugs.kde.org is likely to have more knowledge and can fix things quicker.
Thus every non-openSUSE-specific bug, i.e. bugs that are valid for other distros as well, should have a report at bugs.kde.org. In case it is a really important feature, like e.g. bluetooth support not working at all, or a really important bug, which might already be fixed upstream, then it does make sense to file it downstream (at bugzilla.opensuse.org) too and add the upstream bug report into the URL field. That way the openSUSE team can keep track of showstoppers before a release and crucial fixes after a release.
If your upstream report is set to "fixed" and includes a patch, you should set your opensuse report from "upstream" to "confirmed" for the openSUSE developers to possibly backport the fix.
Enhancements almost always are something to report upstream. If you feel there is something crucial that is in upstream git, i.e. not released yet but already existent, or lacking upstream but really important, then please discuss that issue on the [opensuse-kde] mailinglist or the #opensuse-kde IRC channel.
Useful Crash Reports
Crash backtraces should always get reported with installed -debuginfo packages. If the backtrace contains a text like " This backtrace appears to be of no use.", then you're either missing the debuginfo package or don't have the correct version installed. To install the correct version using DrKonqi, click the "Install Debug Symbols" button on the "Developer Information" page. Note that on Leap 15.1 and earlier it is necessary to enable the "debug" repos manually before those packages can be installed.
More information: KDE Crash Reporting Guide
Specific Hints and tricks
Almost everything is logged to the systemd journal meanwhile, though messages written to stderr end up in $HOME/.local/share/sddm/xorg-session.log and wayland-session.log, respectively.
Debugging of kio_slaves (any problem with a protocol within Dolphin for instance) is a bit more tricky. A description for this can be found here.
If you attach a gdb to a running process, remember that if the process has "[kdeinit5]" in the name, the right executable is kdeinit5.
Debugging Network Management
See our Network Management troubleshooting guide at KDE UserBase for tips on how to diagnose a problem with your networking.