It must be k2tog twice, otherwise repeating the 3rd row until 8sts remain would never decrease any sts (the k2tog would always be compensated for by the yo).
"K2, YO K2tog, K to end
K2, YO, K2tog, TWICE , K10, K2tog, place remaining 18 sts on holder
K2, YO, K2tog, TWICE, K to end
Repeat last row until 8 sts remain"