is there possible to set Ticket standard field as Required fields? for example Ticket Owner must be filled before saved to closed.
In Sales there is possible to block save with ed.setBlockExecution(true) but not in cs.
In Service we have many triggers, but we dont have any which can be directly defined as BeforeSave events, they are mostly triggering after event has occured. Implementing such logic would require you to do this in screen. Some hints can be found in this post. Please note that this will not give you a bulletproof solution as you have many different ways of closing a ticket.
Thanks for the idea in POST. I will set a hiding field x_verify to request, all required fields must be filled and verified for closing ticket, then set it to true in trigger save_ticket. In screen to load scripts, checked by SearchEngine, if closed ticket with false x_verify, should be listed per SetErorMessage. It could be better if the load Scripts in Screen works with getVariable("ticketId") to get current ticket or get trigger to ticket.