When the bitcoin core daemon starts first time it does not have the block database. It must be connecting to other nodes over network. But (I am assuming) it needs to know the at least one live node/peer address (may be more to be robust against down nodes) to connect to the network. Where in code that configuration is accessed? Basically looking for the home calling block of code.
I could try to go through the source
https://github.com/bitcoin/bitcoin but I am sure someone will see this question who can point me to the source file to make it easier.