Do you know that “Năi = ไหน” falls in the same category of “Khrai = ใคร” and “Àrai = อะไร” in terms of Thai grammar? It is considered as such because the answer to all three question words would be nouns.
Năi rawng thaáo khŏrng ther? = ไหนรองเท้าของเธอ
Khun jà pai năi? = คุณจะไปไหน
However, during lesson, I had explained that Năi should be treated like an adjective:
Noun + Classifier + Adjective
Therefore you should be getting something like this:
Noun + Classifier + Năi
The reason I explain in this manner is due to the fact that at times we do use Năi with classifier. For example, we say:
Nák rian khon năi mâi dâi tham kaan bâhn = นักเรียนคนไหนไม่ได้ทำการบ้าน
Khun chôrb kràpăo bai năi khá = คุณชอบกระเป๋าใบไหนคะ
So: Nák rian khon năi and kràpăo bai năi are placed in a position of subject and object, respectively. This follows Thai standard sentence structure of:
Noun + Action (+ Object) (+ Complement)
Now I realize that when we simply put Năi without classifier it sounds very casual (note: not impolite, a little bit colloquial). I would teach my student to use something not too formal, yet not overly casual. Hence it would be better to practice using Năi with the noun and its classifier.
Quiz: Can you try to transform the last 2 examples of Năi with classifier to the one without it?