What are you looking at? のように、前置詞は文の最後に残るのが標準です。前に出した At what are you looking? は、間違いではありませんが非常に硬く、日常ではまず使いません。大事なのは、疑問文にしても前置詞は消えないということ。落としてしまうと文が成り立ちません。
The preposition normally stays at the end: "What are you looking at?" Fronting it as "At what are you looking?" isn't wrong, but it's stiff enough that you'll almost never hear it. The real point is that turning something into a question doesn't make the preposition disappear. Drop it and the sentence falls apart.
疑問詞だけが前に出る
Only the Wh- Word Travels
組み立ての手順で考えると分かりやすくなります。You are looking at that. の that を what に替えて先頭へ出す。at はその場に残る。結果として What are you looking at? になります。移動するのは疑問詞だけで、前置詞は置き去りにされる、と覚えてください。この置き去りが不自然に見えるかもしれませんが、英語ではこちらが標準です。
It helps to build one step by step. Start from "You are looking at that," swap that for what, and move what to the front. The at stays behind. You end up with "What are you looking at?" Only the wh- word travels; the preposition gets left where it was. That stranding may look odd, but in English it's the standard shape.
前置詞は残るThe preposition stays
Who did you go with?
誰と行ったの?
go with someone の with が末尾に残る。The with from go with someone is left at the end.
Where are you from?
ご出身はどちら?
from を落とすと別の意味になる。Where are you? は居場所を尋ねる文。Drop the from and the meaning shifts: "Where are you?" asks your location.
What is this madeof動詞が決める【be made of ＝ 何でできているか】What is this made of? が「材質は何か」を尋ねる定型。文末に前置詞だけが残るのは、of の相手が疑問詞 what になって文頭へ出ているため。?
これ、何でできてるの?
be made of の of が末尾に。素材を尋ねる定型。The of from be made of lands at the end. The set way to ask about material.
後ろに残す(標準)
会話でも書き言葉でも、これが普通の形。The ordinary shape, in speech and in writing alike.
Who are you waiting for?
誰を待ってるの?
前に出す(かなり硬い)
who を前置詞ごと前に出すときは whom に変わる(which や what はそのまま: In which year …?)。式辞や法律文書のような場面に限られる。When who fronts with its preposition it becomes whom; which and what front unchanged, as in "In which year …?" Either way it belongs to ceremonies and legal prose.
For whom are you waiting?
どなたをお待ちでしょうか。
よくある間違い / Common Mistake
×Who did you go to the concert?
誰とコンサートに行ったの?(のつもりで)
○Who did you go to the concert with?
誰とコンサートに行ったの?
with が抜けています。「誰と」という日本語には助詞の「と」が入っていますが、英語では前置詞がその役割を担い、しかも文の最後に置かれるため、書き忘れやすいのです。防ぎ方は組み立ての順序を守ること。まず平叙文 You went to the concert with Tom. を作り、Tom を who に替えて前へ出す。残った with はそのまま末尾に置く。この手順を踏めば落としません。
The with is missing. English hands that relationship to a preposition, and since the preposition ends up at the far end of the sentence, it's easy to lose track of it. The cure is to build the question in order: start from the statement "You went to the concert with Tom," swap Tom for who and move it forward, and leave with sitting at the end. Follow that path and it won't go missing.
Where are you from?ご出身はどちらですかfrom を落とすと居場所を尋ねる文になる。初対面の定番。Without from it asks where you physically are. A first-meeting staple.
What's it like?どんな感じ?like は前置詞なので末尾に残る。好き嫌いの like ではない。Here like is a preposition and strands at the end. Not the like that means enjoy.
Who's this for?これ、誰宛?for が末尾。宛先や用途を尋ねる短い型。For at the end. A compact way to ask about the recipient or purpose.
What are you talking about?何の話をしているの?talk about の about が残る。強く言うと詰問にもなる。The about from talk about stays put. Said sharply, it turns into a challenge.
まとめ / Summary
前置詞は文末に残るのが標準。前に出すのは非常に硬い。Stranding at the end is standard; fronting is markedly formal.
移動するのは疑問詞だけ。前置詞は置き去りにする。Only the wh- word moves. The preposition is left behind.
平叙文から組み立てると、前置詞を落とさない。Building from the statement first keeps the preposition from vanishing.
「文末の前置詞は誤り」という指導は実態に合わない。The rule against final prepositions doesn't reflect how English is used.