I have a Gedcom file that I want to query for a person with at least one missing person.
How can I achieve this?
I am not a software coder but fairly technical otherwise.
There are a number of genealogy database programmes that provide facilities to query the database. Heredis is mentioned in another answer; Family Historian is another option. Both have free trials available, and there may be other products that support query functionality).
If you don't want to invest in another genealogy database but your preferred programme does not yet have query options, you should consider the Gedcom utilties listed at Cyndi's list but be aware that this is a dynamic landscape, and tools may may appear and disappear from it, so if you find one that works for you, be sure to keep the download! You'll find an alternative list (with reviews) at GenSoftReviews.
One example of a class of tools that would almost certainly be useful to solve your problem: If you have access to Microsoft Excel or Access, and are competent at using them, there are utilities that will translate your Gedcom into a format that can be queried in spreadsheets and general-purpose databases. Gensoftreviews (search for Utilities with the text "csv" in them) will lead you to some possibilities such as GedXlate or Oxy-Gen
With Heredis, you can do that easily.
The Smart Search feature allows to query your data through combined search criteria. For your specific need, see the screenshot above, I've chosen "Relations" -> "Ancestry" -> "Only one known parent" = yes.
You can even do more complex queries like this one:
Here, I've combined three criterias:
Heredis is available on Mac and Windows and a demo version is available to download if you want to give it a try.