  The digital twin channel (DTC) is crucial for 6G wireless autonomous networks
as it replicates the wireless channel fading states in 6G air interface
transmissions. It is well known that the physical environment influences
channels. A key task for accurately twinning channels in complex 6G scenarios
is establishing precise relationships between the environment and the channels.
In this article, the radio environment knowledge pool (REKP) is proposed, with
its core function being to construct and store as much knowledge between the
environment and channels as possible. Firstly, the research progress related to
DTC is summarized, and a comparative analysis of these achievements on key
indicators in digital twin is conducted, proposing the challenges faced in
knowledge construction. Secondly, instructions on how to construct and update
REKP are given. Then, a typical case is presented to demonstrate the great
potential of REKP in enabling DTC. Finally, how to utilize REKP to address open
issues in the 6G wireless communication system is discussed, including
enhancing performance, reducing costs, and keeping a trustworthy DTC.
