Not related to any of the above surnames, but happened to notice that 'feathers were ruffled' when Rick Thoma mentioned this new forum was not necessary. I can see both arguments. Many surnames on this and other forums that start with Y or J can be considered from the same long-ago roots, but people who are not aware of the linguistic changes over the centuries may need to start at a more basic level.
In Canada where I live, YOUNKER (132 listings) seems to be the most common spelling variation in the phone book - www.canada411.com -, and interestingly 50% of all of them are in Canada's smallest province, Prince Edward Island. Another 18 in Canada spell it YONKERS (as in the NY community north of Manhattan). I strongly suspect they arrived there between 1760 and 1783/4 as land grantees, or decommissioned German or other Protestant military folks, either from the French & Indian Wars of the 1750's, or those fleeing after the Rev War ended in 1783. Many were Loyalists (called 'Tories' in USA) who wanted to stay under the English King.
It's very likely there were two lines in the 1700's: from England (with continental European origins) after being there for many generations; or directly from Switzerland, the German States (no Germany until 1870), or Holland. Were some lines perhaps French Protestants (Huguenots) who had fled religious persecution ?
Bottom line here - pursue this spelling, but check out all the other ones too. Sooner or later, you will spot information that just HAS to be your family line.