Klein gives the following etymology for naknik:
Coined by Eliezer ben Yehudah (1858-1922), from Aramaic נוקניקה ( = a kind of sausage), which is borrowed from Late Greek loukanika, from Latin lucanica (= a kind of sausage invented by the Lucanians), from Lucanicus (= Lucanian), from Lucani (the Lucanians), a people in Lower Italy.
The one example of nukanika in the Rabbinic literature that I was able to find is in Yerushalmi Shekalim, Chapter 7:
נוקניקה אשתכח בכנישתא דבולי אתא עובדא קומי רבי ירמיה אמר יתחכמון סקורייא עבידתהון
Some commentaries translate this as follows:
A bottle of wine was found in a synagogue in Buli. The case came before Rabbi Yirmiya, and he said let them identify the bottle by the color.
This reading seems to influenced by the previous sentence, which also deals with bottles of wine, and also an assumed connection between נוקניקה and קנקן (bottle).
However, Jastrow identifies nukanika as sausage, and Sokoloff, DJPA, s.v סיקייר translates the section like this:
A sausage was found in the synagogue. The case came before R. Yeremiya. He said - let the sausage makers (Latin insiciarius) recognize their product.
(In addition to lucanica, isicia was another word for sausage in Latin.)
Naknik still has culinary cousins in the Italian lucanica and the Greek loukanika (but naknik is generally more kosher...)