Open a command prompt, change to the c:\jRDC2 folder and try
C:\java\jdk-11.0.1\bin\java.exe -jar jrdc.jar
Note: you may have to adjust the directory in the above command to wherever java.exe is located
If everything works (no errors are displayed. Note: you need to run the test link to see if jRDC2 properly connects to your DB), you should see the output in the prompt. You can stop jRDC2 server with Ctrl+C
If that works, then you can create a batch file in the jRDC2 folder with
C:\java\jdk-11.0.1\bin\java.exe -jar jrdc.jar > stdout.txt 2> stderr.txt
as the content. Test the batch file by running it.
If that works, then proceed to configure nssm to run the batch file for the service