Green’s Dictionary of Slang

the jaw; the face.

1854		‘Cuthbert Bede’ Adventures of Mr Verdant Green (1982) II 166: While to another he would say, as a fact not to be disputed, ‘You napp’d it heavily on your whisker-bed, didn’t you?’.
1855		(con. 1852) Fights for the Championship 249: He [...] reached Orme’s lef whisker-bed, but napped it heavily on the sore spot.