How do nodes communicate over Lightning network? I read the following article and watched below video.

https://medium.com/@melik_87377/lightning-network-enables-unicast-transactions-in-bitcoin-lightning-is-bitcoins-tcp-ip-stack-8ec1d42c14f5

https://www.youtube.com/watch?v=Ug8NH67_EfE

On those media, they say that payment channels are based on just TCP/IP connection (unicast) not p2p.

In Lightning network's white paper, there is no explanation of what method is used to establish payment channel between two nodes.

What method is used for establishing payment channels ? traditional TCP/IP way or p2p ?
You are confusing two things here: payment channels and network communication. A payment channel is really the set of commitment transactions and their revocations. It is unrelated to network communications and the participants in a payment channel do not need to communicate via one specific way.

The network communications that nodes use to talk to each other (e.g. to update payment channel states) use TCP in a P2P manner. Like Bitcoin, a node establishes a TCP connection to other nodes, and those nodes have connections to other nodes. P2P is not a communication standard like TCP and UDP, rather it is a model of the network's structure and is a concept.