I found an article on this subject.
This phenomenon (the omission of a substantive verb) is called "ellipse", this is a rhetorical and stylistic expression. When a word or a phrase is omitted, and this causes a lack , what they can be inferred from the context. This is also common in everyday speech. The article in Hungarian: http://www.e-nyelv.hu/2014-05-25/letige-elhagyasa-ellipszis/
This sentence is not wrong though, it's just colloquial, without any kind of stigma. It's not rare to drop "van" in "hol" sentences, I personally even feel some nuanced difference in connotation - leaving out "van" sounds like you are searching for them, maybe you are a bit impatient already, "I want them to be here" rather than just literally asking about some position.
I sympathize! And to myself each day, I keep thinking the answer is: more practice. Eventually, it comes. Just today I was listening to one of the sentences, and it was not making sense to me. Then suddenly I realized what part of it actually was; it sure made me a little glad. I am also wondering why Duolingo has only whole audio sentences in this Hungarian course. In other courses, one can hear whole sentences, but also hover over individual words and hear each word separately. But maybe in Hungarian it is important to hear the words without pauses. I find it challenging! Also, I have a little notebook, and the first time I do a lesson, I write down all the sentences. That has helped me very much! It takes a little time, but I find I can look at them without the computer--and just writing them down helps me remember them a bit better. (I don't write down the English translation.) I even look at what I've written when I do a lesson over! And over. And over. Hungarian sure is different!
I dont know where to post this request or advice. A lot of times, when I must write in the language that I studies, when I finish to write and I ask clik to know if I give a good response or not, I cannot read what I have written. It is not very good for a learner to hide immediately replay, because, even if I reply good, I want read again wgat I wrote to remember better. So, please, give this little correction to your very nice software. Congratulation. Wxcuse me for not very good english. Bye