Literally: He doesn't know a dirty fingernail; i.e., someone who knows very little or nothing about something.
⚙ Usage examples pulled from the Virtual Library
In Balinese: Tusing ada buin akejepan, pesu anak tua maawak gede, bok magambahan gempel, paningalanne nelik, munyine gede gara, nyonyone lambih, basang gede, batis mabulu, tur kuku lantang.
his/her nail, suffix {nne} states ownership or clarifying the words followed. Almost the same as possessive pronoun in English. In the word 'kukunne' can be interpreted as 'his/her nails'