Must be Hamarnik as opposed to Hamornik, as the second syllable is stressed here (unstressed o is pronounced somewhat like an a). The Ukrainian pronounciation is hah-MAHR-nick, the Russian would be gah-MAHR-neeck. Looking at the Russian Wikipedia articles of famous Gamarniks I realized that all of these people were both Jewish and born in Ukraine. This lead me to suspect that the etymology is probably Yiddish. I also stumbled upon the actual article of the surname's etymology. It turns out that it is either from German/Yiddish Hammer, so a metalworker or smith. Alternatively, it could be from Aramic, Gamr, meaning "Study". Hope this helps.