@Mary3709, first: this is a public forum. Its contents show up in search engines nearly immediately. It's a bad idea (and against the "code of conduct") to put your full email address in a posting here. If you're still within the four-hour edit window, you can click the "ellipses" at the top right of your post, choose "Edit", and delete your address. If that button is no longer there, then you can use the "Flag" button at the bottom right of your post to alert a moderator to the need to edit out your personally identifying information (PII).

Second: genealogy is about a whole lot more than just surnames. Many totally-unrelated people could have exactly the same surname -- and conversely, the vast majority of your ancestors had a different surname from yours. (For most people, out of 126 direct ancestors on a 7-generation fan chart, 120 have a different surname.)

Third: it's not clear to me what names and places you're asking about. "Stankovic" is clearly a surname, and "Dreznik" is a place, but the Croatia supplement to the 1913 gazetteer of Hungary lists Drežnik in Modrus-Fiume county, Brezovički Drežnik in Zágráb county, Gornji Drežnik in Pozsega county, and Podokićki Drežnik in Zágráb county. Which of these did you mean? Likewise for "Karlovac": there's Karlovac (Károlyváros) in Zágráb, Podgorački Karlovac in Verőcze, and Viljevački Karlovac also in Verőcze. "Vuksan" doesn't occur in the gazetteer supplement; the closest it gets is Vuksani in Zágráb.

FamilySearch has the "Croatia Church Books" collection (https://www.familysearch.org/search/collection/2040054), but it's only (very) partially indexed, so it's not surprising that the search is not coming up with a family near Zagreb with the right names.

I see on the Family Tree (https://www.familysearch.org/tree/person/sources/GJDV-3BQ) that you have not so far tracked down John/Janko's circa 1909 arrival that's mentioned in the 1920 census; perhaps you could start with looking for that, to see if it names a birthplace or at least specific town of residence?

The WWI draft registration that's a hint on John's profile seems doubtful to me: Lyndora isn't Pittsburgh, and the couple in the 1920 census had a six-year-old daughter, so they would've been married by 1917-1918. (Although perhaps it'd be possible to find out what the "FSW Co." did in circa 1917 Lyndora, just to make sure.)

Yes, I know you asked about John's parents, but we can't get to them without more information about John. It's the general principle in genealogy (and every other form of research, really): you start with what you know and work your way toward what you don't yet know.

As I said, there are some records available for the general time and place you think is relevant, but you haven't told us -- and I haven't found -- why you think those times/places are relevant, so it's basically impossible to narrow things down. As I also said, most of the records have not been indexed, so without precise places and dates, the chances of finding a relevant record are approximately nil.

I will try one more time before giving up.

If that random-looking assortment of places near Zagreb is accurate, then there is a very good chance that the relevant records have not been indexed. This means that they cannot show up in a search by name. They're not in that database.

There are ways to find records that have not been indexed, but they all start with narrowing the field somehow, to make the task managable. For example, if you have a precise religion, birthdate, and birthplace for a person, then it's actually relatively simple to browse through the relevant church register images to find the right birth-and-baptism record. If one or two of those pieces of information is missing, the browsing will take longer, but you may still have success. However, if they're all missing, as here, the task becomes, if not precisely impossible, then close enough to it to make no difference.

So, we need to fill in more about John, because if we find his birth/baptism, then we should be able to work our way to his parents' marriage. I figure I can guess a religion based on the population information in the gazetteer -- once I have a candidate birthplace to look up in said gazetteer. You gave some placenames in your first comment, but you have been insisting (loudly) ever since that you don't have that information, never mind telling us where it came from.

My capacity for re-inventing the wheel is limited. Hence my repeated queries: what do you actually know already about John? Where in FS's vast sprawl did you encounter Stefan as his father's name? Where did you get his mother's name? Do any of those sources perchance identify a birth town and/or birthdate for John? What was your source for those three placenames in your first comment?