The solicited node multicast address is known because the IPv6 RFC standards have established a “rule” in how to form the solicited node multicast address based on the IPv6 addresses that is needing to be queried. The rule states that solicited node multicast address is: FF02::1:FFXX:XXXX where X is the last 24 bits of the IPv6 target address. This means you take the last “half” of the next to last hextet, and the entire last hextet and append it to FF01::1:FF. See example below.
The last thing you would need to know is that there is also an IPv6 RFC rule for creating the layer 2 address for any IPv6 multicast address. That rule states the address is 3333:FFXX:XXXX where X is the last 24 bits of the multicast address
Example: Let’s say Host A has just booted up, and wants to use the local IPv6 address of FE80::0200:0BFF:FE0A:2D51. Host A needs to determine whether another host is using this address before it is allowed to start using it. In this case, a Neighbor Solicitation called DAD (duplicate address detection) is used. Here are the layer 3 and layer 2 addresses this DAD would use:
Source Address: :: <--------- Host A isn’t allowed to use a layer 3 address yet
Destination Address: FF02::1:FF0A:2D51 <--------- This is the result of the IPv6 RFC rule for crafting a solicited node multicast address
Source Address: <Host A’s MAC address> <--------- Normal Ethernet operation here
Destination Address: 3333:FF0A:2D51 <--------- This is the result of the IPv6 RFC rule for crafting layer 2 addresses from an IPv6 multicast