I have answer about why some people in malaysia say than na in 台湾话大词典。It can than ni 尔 as well.The hanzi is 端仔=表示完全,确实。The hanzi could be wrong.
我 than na 要 =我一定要
than na 无影=完全是假的
你 than na 不肯=你一定不肯
The author saysome it wrongly as kan na
Yes, gua2 ma7-cai1 我[也]知 is the proper Hokkien for "I also know", not gua2 pun2-cai1. Yet gua2 pun2-cai1 can be 我本知 "I have known" = gua2 pun2-cia*5 cai1 我本[成]知 "I have been knowing it" = gua2 guan2-pun2 tio8(ciu7)-cai1_a1 我原本着(就)知了 "I have been knowing it from the beginning".