Hi,
the jar file can be opened with (almost) any zip/unzip tool. In that jar, you will se a directory structure, the file path is:
org\enhydra\shark\xpdl\resources\TC-1025_schema_10_xpdl.xsd
To redirect the web-calls from wfmc.org to your local web-server, you need to modify the etc/hosts file. If you have linux machine, this file is in the /etc direcory. In case of Windows, this file is in C:\Windows\System32\drivers\etc.
Usually the first line conatins the "localhost" reference, modify this line to something linke this:
127.0.0.1 localhost wfmc.org
By this modification all calls which address the wfmc.org will be sended to your local web-server. If you put the extracted xsd to the proper place (/standards/docs), joget will find the required xsd.
If these things above aren't clear, it's better to ask help from a system administrator of your organization.
Tibor