The first command lists all nodes and their performance metrics sorted by the highest number of CPU. The second command takes that first row. Finally, the third command takes the first column of data.
cluster1-controlplane ~ ➜ k top nodes --sort-by=cpu --no-headers
cluster1-controlplane 577m 1% 1008Mi 0%
cluster1-node01 62m 0% 464Mi 0%
cluster1-node02 57m 0% 532Mi 0%
cluster1-controlplane ~ ➜ k top nodes --sort-by=cpu --no-headers | head -n 1
cluster1-controlplane 569m 1% 1009Mi 0%
cluster1-controlplane ~ ➜ k top nodes --sort-by=cpu --no-headers | cut -d' ' -f1
cluster1-controlplane
cluster1-node01
cluster1-node02