I assume you had a brief idea about DHCPv6 and ICMPv6.
DHCPv6 Client will usually obtain the dynamic IP address through 4 messages. Those messages are SOLICIT, ADVERTISE, REQUEST and REPLY. So during these message transaction the DHCPv6 client can also request the DNS server address using the ORO(Option Request Option) option. If the client request is accepted by the server then reply packet will contains the DNS Server address. Like wise the client can also request other ORO options.
The IPv6 client can also obtain the dynamic IPv6 address using other mode called SLAAC mode(Stateless Auto Address Configuration). The IPv6 client will usually perform the SLAAC mode when the managed bit flag is not set in the received router advertisement(RA) message whereas if the managed bit is set then client will use DHCPv6 client. In the SLAAC mode itself there are 2 ways to obtain the DNS Server address. First one is through RA message itself and it is called as RDNSS and other method will be used when the received ICMP RA message contains the other bit flag set. If the other bit flag is set then DHCPv6 client will be used for getting the additional information's like DNS Server address.
The final method is of-course the static configuration of the DNS Server Address.
