The Fonkert name is rare. Even in The Netherlands, it is uncommon.* If you encounter a Fonkert anywhere in the world, you can be nearly certain that her or his family origins are in the Hoekse Waard of Zuid (South) Holland. (A waard is low-lying land between river that is subject to flooding unless protected by dikes).
The Fonkert name, spelled "Fonckert," first appeared in Rhoon, on the island of IJsselmonde just north across the Oude Maas from the Hoekse Waard. (The Oude (old) Maas and Nieuwe (new) Maas are rivers the flow just south of Rotterdam in the Rhine-Maas delta.) Three Fonckert brothers -- Dirck Adriaensz, Willem Adriaensz, and Adriaen Adraiensz** -- lived in Rhoon in the late 1500s. Their apparent father, Adriaensz Willemsz, is mentioned in connection of several pieces of land in Rhoon between 1572 and 1594.
The Fonckerts likely came from somewhere else. One possible origin in the village of Driel, located on the south bank of the Nederrijn (Lower Rhine) near Arnhem in Gelderland, about two miles from the modern Netherlands-Germany border, and only about 60 miles upstream from Rhoon. Two pieces of evidence suggest Driel. First, the wife of Adriaen Willemsz Fonckert was a granddaughter of Doen Beijensz van Driel -- Doen, son of Beijen, of Driel. A Dutch genealogist has suggested that Doen Beijensz may have come from the manor of Driel in Gelderland. Second, a family named "Fonck" lived in Driel in the 1500s. Dirck Fonck Dirksz was schepen of Driel in 1566. During the reformation in the 1500s, a religious boundary developed near Driel, with Catholics to the east and Protestants to the west. This might explain the movements of Foncks-related families west down the Nederrijn (see https://nl.wikipedia.org/wiki/Driel#Vroegste_geschiedenis).
The "ert" name-suffix occurs in other German and Dutch names (e.g., Dekkert, Eckert, etc.). The suffix "ert" is attached to verbs to indicate someone who does something, much like, in English, a baker is someone who bakes (in German, Beckert is a baker). So, it is possible that a Fonckert is someone who Foncks. Some 20 years ago, a German genealogist*** told me that "fonck" might derive from the German verb "funck." He explained that as old German moved in the direction of modern German, shifts of "u" to "o" were common. In modern German, the noun "funk" means radio, and the verb "funken" means to transmit or broadcast, or in other situations, to spark or flash. The genealogist explained that blacksmiths or hammerers were called "funkers" because they made sparks in their work. Dutch is closely related to German, and in modern Dutch, the verb "fonkelen" means to sparkle or scintillate.
Nemerous Fonck or Fonk families are recorded in the Rhineland area of western Germany in the 1700s and 1800s.*** The name "Vonk" (pronounced "fonk") also appears in the same area. The names Vonck and Vonk were also common in Zuid Holland.
Is is possible? Is a Fonkert really a Smith? A plain, old ordinary blacksmith? Possibly from Driel.
I'm not certain of any of this. I'm not sure I ever will be. I'm not even sure it matters. For now, it's just fun to explore the possibilities.
* A search at www.detelefoongids.nl finds only 24 Fonkert listings.
**The "sz" ending stands for "szoon," indicating the name is a patronymic. Thus, Dirck Adriaensz is Dirck, son of Adriaen.
*** Fred Rump, Beverly, NJ; email 18 November 1995.
**** The "Fonck" name and variants appear in these time periods and regions in the International Genealogical Index.
NOTE: The Family History Library (www.familysearch.org) has microfilm of both Catholic church records beginning 1633 and Protestant records beginning 1650for Driel.
Sources for early Fonckert history:
A. P. van den Hoek, Genealogie van het Geslacht Fonkert.
K. J. Slijkerman, "Het Geslacht Coorneef (Koreneef enz.) te Rhoon, Poortugaal, Oudenhoorn en Spijkenisse," Deel (Part) 6 of Geslachten an het Eiland Ijsselmonde (Rotterdam, 1991).
J. J. Vervloet (in association with the Workgroup Doen Beijensz.), De Parenteel van Doen Beijensz. (Rotterdam: 1989).