I followed the instructions at https://github.com/WolframResearch/WolframLanguageForJupyter/blob/master/README.md
wolframscript configure-jupyter.wls add
but I get
configure-jupyter.wls: Provided Wolfram Engine binary path does not exist.
so I tried
wolframscript configure-jupyter.wls add ["/usr/local/Wolfram/WolframEngine/12.0/SystemFiles/Kernel/Binaries/Linux-x86-64/WolframKernel"]
where the path shown is the result of starting wolframscript and doing
First[$ComamndLine]
and get the same result.