Green’s Dictionary of Slang

nob n.4

[? dial. nob, an interloper]

in cribbage, the knave of trumps.

[UK]Hotten Sl. Dict.
[UK]Sl. Dict.
[UK]N&Q Ser. 7 28 Apr. 340: The old name of cribbage was ‘noddy.’ ‘Noddy,’ being the name for the knave, has been contracted into nob .