Hello,
I've moved your post to the new thread in Sony Xperia Z3 forum.
my sony z3 bricked when flashing new rom by flashtool
Can you post flashing log?
I've try disassembly, found testpoint as you mention (PC regconised ESMC device)
You can make a good picture of your main board and mark testpoint for future reference - i think a lot of people will be interested to know where it's placed 
So, can I use this method for it?
No, you can't flash that phone using testpoint (s1 emergency mode) at the moment.
If yes, where I can find needed file to flash?
I've downloaded stock rom (23.0.D.1.123 for z3 D6616- lollipop) , but cannot found the needed file. Help me, please!
In your case you can repeat flash procedure using Flashtool or you can try to repair firmware in your phone using PC Companion. Or you can visit nearest service centre (or use our sony ericsson online service) and your phone will be flashed using professional service tool if boot / trim area is not damaged. And for the future - if flashing process is failed - just repeat it and if needed - fix the core issue. There is no point of disassembling phone, loosing waterproof feature and warranty... 