Let give my script a try. I did a quick test in PDI, it works well from my end.
var prefixToRemove = "KOK - SIDK - "; //prefix
var tenantCI = producer.getDisplayValue("cmdb_ci"); //tenant CI
tenantCI = tenantCI.replace(prefixToRemove, ''); //remove prefix
var short_description = producer.Issue_Category + " - " + "Tenant: " + tenantCI; //build short description
current.short_description = short_description.trim(); //set short description
Cheers,
Tai Vu
