在香港, 納粹是違法嗎?? (請指出是違反那一條法律)

Everyone in Hong Kong have the right to free speech as guaranteed by the Basic Law, however, under HK Laws. Chap 245 公安條例 Sec. 17B 公眾地方內擾亂秩序行為
(2) 任何人在公眾地方作出喧嘩或擾亂秩序的行為，或使用恐嚇性、辱罵性或侮辱性的言詞，或派發或展示任何載有此等言詞的文稿，意圖激使他人破壞社會安寧，或其上述行為相當可能會導致社會安寧破壞，即屬犯罪，一經定罪，可處罰款$5000及監禁12個月。
So it depends what would've been said. If, for example, incite others to kill another racial group, then no only the above law would've been broken, it would include:
HK Laws. Chap 212 侵害人身罪條例 Sec.9A 危害種族
(2) 犯危害種族罪的人循公訴程序定罪後─ (a) 如該罪行包含殺人，須處終身監禁； (b) 如屬其他情形，可處監禁14年。