did ‧ dly /ˈdɪdli/ BrE AmE ( also did‧dly‧squat /ˌdɪdliˈskwɒt $ ˈdɪdliskwɑːt/) American English informal noun
[ Date: 1900-2000 ; Origin: Probably from doodlysquat 'nothing' (1900-2000) ]
not know/mean diddly to know or mean nothing at all:
Brad? He doesn’t know diddly about baseball.