Which animal does supply milk(?)

What animal produce milk?

Uly, could you explain why we don't use a help verb here?

Like what?

Does.
What animal does produce milk?
would be ok to say? If not, why?

A: Have you ever had crocodile milk?
B: Crocodiles don’t produce milk.
A: What animal DOES produce milk?
B: Cows.

So, saying "What animal DOES produce milk?" is correct? Or only correct when it was an answer to a direct question?

It’s used to contrast: Russ doesn’t speak Chinese, but Alan DOES speak it. If Russ doesn’t understand Chinese, then what language DOES he understand?

Ok, we can use DOES to contract something that was said before. But if I'm a teacher in class and want to ask the kids, should I say:
What animals do produce milk?
OR
What animals produce milk?

No, it’s not to refer to what was said before, it’s to emphasize a contrast. For instance, if crocodiles don’t produce milk, then what animal DOES produce milk?

So, if I just asking a general question should I say:
What animals do produce milk?
OR
What animals produce milk?

What animals produce milk?

Hm, so no help verb. I've always thought we don't use help verbs only when asking WHO... (Who sent him?). But now I see there are instances when we can ask WHAT question without using a help verb... Never knew...

I’m not sure I know what you mean by helping verb. DO is an contrasting element: If this isn’t the case, then that IS the case. If he doesn’t do this, then who DOES do it? I just don’t know how to say it in Russian.

Maybe I'm not using help verb definition correctly. E.G. I wanted to know why in the phrase What animals produce milk? you did not use DO. For example:
What DO you think about Zoya?
What DOES this tune sound like?
What DOES it mean?
What DOES she look like?
What DO they think about him?

In all questions above we use DO or DOES.
I'm confused, why saying "What animals produce milk?" we didn't use DO?

Ah! It’s because WHAT isn’t a pronoun in that question, it’s an adjective describing ANIMALS. In other words, in “what animals produce milk?,” WHAT doesn’t mean что, it means какие.

Hm, then we shouldn't use DO in this question - What cars do you like? coz it describes cars. But use still use do.
Or what girls do you like?
we would not say What girls you like?
confused...

The difference is that in this sentences, WHAT GIRLS and WAHT CARS are the objects of the verb. In WHAT ANIMALS PRODUCE MILK, the animals are the subject of the sentence.

so confusing but thank you for your patience explaining this.

Look at this - the last sentence:
https://lingvolive.com/posts/1418618