Hi Laksen,
The 'Z' in the front of the transaction code indicates that it is a customer object, i.e. a custom transaction code created in your system, not part of the SAP standard. Therefore, we can't know precisely what it does, and that's also why it won't show up in a search on Google or SCN. It's specific to you.
However, it's very likely a modified clone of standard tcode KO8G, which is for settlement of internal orders. Or, it might not be modified at all, but just setup to call KO8G with a standard variant to preconfigure the selection screen.
Have a look at tcode SE83, Maintain Transaction, to lookup the program that your ZKO8G calls and any variant it uses. Then you can look up what that variant does in that program.
Cheers,
Matt