What IP address of a VPN server does my provider see?

If a connection is made through a single server the explanation may be given in such a way: your IP address passes to the VPN; your VPN connects to a site. VPN’s IP sees both the provider and the site. If you are accessing through a double VPN, then your IP address passes to the VPN 1 and then to the VPN 2 and only after that it connects to the chosen site. In the later case your provider sees the VPN 1 while the site sees the VPN 2.