I want: ping server on my PC by it domain name from remote.
I have:
The port forward that you set up will not allow you to use ping (in that case, you're doing an ICMP forward). But it looks like you don't want to ping, but rather access a web page on port 3000.
Troubleshooting steps:
Try it locally first - on another computer on your home network, try to reach http://, in your question this would be http://200.300.1.15:3000/. If that doesn't work, none of the rest will work - check to make sure your computer's firewall is allowing incoming TCP requests on port 3000 (or turn the firewall off for testing).
Next, try it directly by your IP from outside your home - http://94.154.220.216:3000/. If local works but this doesn't, then your port forward it not working, ISP is blocking incoming TCP requests, or something else.
And then finally, ping my_domain.duckdns.org, and make sure it resolves to your IP (94.154.220.216). At that point you should be able to hit http://my_domain.duckdns.org without a problem.