Kernel Task is using 1000% of The CPU on macOS Catalina
Kernel_task is a dummy process which takes up CPU resources from other applications in order to cool the system down. So I would look at your system's cooling, maybe use fan tools such as Mac Fan Control and perhaps disabling turbo boost with a tool such as TurboSwitcher. Also on some MacBook Pro's you can cool the system a bit by using a TB3 port on the right-hand side to charge from rather than the left.

Some other issues related to Kernel_task problems.


Update software (so bugs get fixed)
Check for malware. 
Adobe Flash! if you have this uninstall it is well known using up CPU resources. It is not needed anymore.  
Boot into safe mode see if that solves the issue
If #4 works try uninstalling third-party software with kernel extensions (kexts) by using AppCleaner or CleanMyMac X,
find them using terminal  kextstat | grep -v com.apple and match them to the software packages. Do not remove Apple's, hence the command line filters them out of the listing of extensions.
Use System Preferences -> Users &amp; Groups -> Login Items and remove those applications you don't need to start upon login.
Clean out your system using a tool like CleanMyMac X and uninstall applications you no longer use.
Try resetting NVRAM
Upgrade macOS
10.Reinstall macOS