I have found a possible way to find an unknown class name for use with "show-generic-objects"
First, look at the type of the object, using the show-object uid uid command:
> show-object uid 6c488338-8eec-4103-ad21-cd461ac2c472
name: "Check Point Data"
domain-type: "data domain"
Once you have the type, in this case "RulebaseAction", query the database directly for a possible match, grep lowercase and uniq to remove duplicates:
[Expert@cp8020-mgm:0]# psql_client cpm postgres -c "select objclass from dleobjectderef_data where objclass like 'com.checkpoint.objects.%'" | grep -i rulebaseaction | uniq
com.checkpoint.objects.rulebase.RulebaseAction <<<<<<< I was looking for this
Very useful info to search and query almost any object in the database using the rest API show-generic-objects