nape, back of the neck
Y tú tienes una encantadora y delicada nuca.
And you have a lovely, delicate nape.
— Fresas salvajes (1957)
Bájate los calzoncillos, manos a la nuca y agáchate.
Pull down your underwear, put your hands behind your head, and squat down.
— Bajocero (2021)
Los ojos que tienes sobre tu nuca.
The eyes you have on the back of your head.