Why does it say "Kinah Hi"?
Radak: It said so at the beginning (2), and also [here] at the end.
What do we learn from "Kinah Hi v'Konenuha"?
Radak: Say it in it a voice of Kinah (lamentation).
Radak citing Targum Yonasan: The Nevu'ah is a Kinah, and it will be for a Kinah 1 .
Malbim: Make a Kinah over the first fall [of Egypt] outside its land, and the young lion and Tanin that was cast to the Midbar.
I.e. people will say it to lament. (PF)
Which Bnos ha'Goyim will lament with it?
Radak #1, Targum Yonasan: People of villages of Goyim.
Radak #2: Women; the custom is that women lament - "v'Kir'u la'Mekonenos u'Svo'enah" (Yirmeyah 9:16). There is a Dagesh in the latter Nun in Tekonenah, for the Nun of feminine plural conjugation is omitted. Both Nunim are from the root; it is a four-letter root.
Radak #3: They are congregations of Goyim. This is like Bas Tziyon, Bas Edom.
Malbim: Make a second Kinah for the second fall, when Kasdim came to Egypt. Many Goyim fell with it ? all its helpers and supporters. Their daughters will lament. This is a general Kinah, for the stars, sun and moon that were covered in a cloud and dimmed.
Why does it add "v'Al Kol Hamonah Tekonenah"?
Malbim: This is for the third Churban, in which Egypt and all its multitudes were totally destroyed. All the luminaries were darkened, and there was thick darkness on Egypt. Also this, Bnos ha'Goyim lamented, for no Egyptians remained 1 !
There was a remnant ? Egypt will return after 40 years, and we find that Minyomin in the days of the Tana'im had the law of a Mitzri convert (Yevamos 76b)! Perhaps a miniscule number remained, and they would not suffice to properly lament Egypt. (PF)