I use a VPN service that is connected to a server in another country, however this VPN service does not offer control over my DNS requests to block some sites so I preferred to use another DNS resolver that has this function.
My question is: When I access my VPN’s website, it accuses that a “DNS leak” is occurring. Can the DNS provider know my real IP address, or does it only know my VPN’s IP?
Yes, you can configure non-router DNS in your DHCP server or you can manually set DNS on individual hosts. For a VPN you want to make sure the VPN connection has DNS manually configured.