Hello Devaprem
If you have a NAT translation between two addresses configured on a router, you don’t require any of those addresses to have a routing table entry in that specific router. These addresses are considered directly connected because they are associated with specific interfaces. For this reason, you don’t have to explicitly configure them for routing. However, other routers on the outside must have some routing information to be able to reach the 20.20.20.20 IP address but this is independent of NAT.
In general, when a packet arrives on an interface from outside to inside, it will translate NAT first and then route. More information about the order of operations in routers can be found at the following Cisco documentation.
I hope this has been helpful!
Laz