I'm not sure that classifiers are what the question asker was looking for. While I can't say that I actually know what they're asking (and I know no Thai at all), the way it's phrased makes it sound like they are asking for either a question particle or an interrogative pronoun.

@Moshi - That was my first impression from the question as well, but I reconsidered as part of celebrating the Codidact anniversary. A classifier is obligatory in a simple question of the "how many" type. There's also "กี่" which means simply "how many" which would hardly strike a fluent speaker of English as "special". And there's no third special word in the Google translate dialect of Thai.

@Moshi I strongly suspect that Jirka's answer is right. It's one of the harder things about Thai. English has classifiers ("How many pairs of pants?" and "How many lengths of string?"), though rarely obligatory and nowhere near as many as Thai. In addition to paired things, string-like things, and four-legged things, there are also round things, person-like things, two-legged non-person things, flat things, and on and on.

Michael‭ I have no real way of telling one way or the other as I don't know Thai, and the questioner has left Codidact so they can't elaborate, so this is likely the most useful answer we're going to have.

As an aside, there is something to be said about calling those words in English "classifiers" (which somewhat implies them being syntactically distinct from normal nouns), but yes, those are the usual analogies drawn.

By the way, to mention people on Codidact, you should click the dropdown after typing in @... This creates the special mention like in this comment which actually notifies the user.

An arguably obligatory use of classifiers (whether we call them that or not) in English is when counting uncountable nouns. While ordinary nouns are used for that purpose, the choice of the specific noun is often idiomatic... leaving the speaker with no other choice. Conversely, the list of Thai classifiers referenced from the answer concludes with "...common words may occassionally be used as classifiers."

To appreciate that this is both similar and different from the situation in Thai, let's check the classifier represented in the answer as "animal" (for counting of elephants, chairs, and, incidentally, of pants, too). Is it (also) an ordinary noun in Thai? Well, yes, but then it means "body", it does not mean "animal" if used, say, as the head of a subject. Now, apply the same exercise to the English word "length" and you may spot that the classifier meaning and the "regular" meaning aren't identical, either.

Let's not get carried too far away from the question at hand, however. Thai grammar needs to invoke the concept of classifiers precisely because they serve way more functions than counting; counting is just a textbook example of a context where they are obligatory. English does not come anywhere close to that, regarding the grammaticalization of its (say) idiomatic counting words.