Hello Xino and jheltone, I am really sorry to sound incomplete and confusing: it is because this is my first-time experience with Linux, and that is why every step draws blood from me 
- and there is no one around I could have possibly ask for help.
As of now I created the dhcp-client.conf file according to the link provided by Xino (thank you!) and then restarted NetworkManager. It seems like nothing changed. I judge by the fact I still cannot ping anything outside. Looking into the logs I can see that there is nothing received via the ens1f0np0, despite that there were a lot of sent packages.
I compiled the “combined” screenshot made of the responses to all commands you recommended to me:
Therefore it seems like the configuration matches the requirements, the physical layer is functional (I connected my laptop to the same cable I insert into the Linux server - and it connected to the network no problem), DHCP seems to be enabled - but it failes obtaining the lease and therefore, to establish connection. What can be the reason for that?
Thank you for your time and input,
Mike F.