To open the YSQL shell (ysqlsh), run the following.

$ kubectl --namespace yb-demo exec -it yb-tserver-0 -- sh -c "cd /home/yugabyte && ysqlsh -h yb-tserver-0 --echo-queries"
ysqlsh (11.2-YB-2.23.1.0-b0)
Type "help" for help.

yugabyte=#