How bitcoin daemon search nodes to connect? How bitcoin daemon search nodes  to connect? What file in github responsible for this? How they often change? How is the veracity of the data of these nodes checked? Bitcoin daemon have function not save blockchain data on device?
How bitcoin daemon search nodes to connect? What file in github
responsible for this? How they often change?

Bitcoin use peer discovery to find nodes to connect to, some are hard coded in the file bitcoin/src/chainparams.cpp of the bitcoin core client available on github.
You can find more information here:
https://stackoverflow.com/a/19956156/1616622

How is the veracity of the data of these nodes checked?

There is no need to check them manually that is the beauty of decentralized blockchain, if someone try to trick other nodes by using wrong data like a wrong blockchain the other nodes will see it because of the bitcoin protocol and ban him