A1
か — the question particle
How か turns a Japanese statement into a question without reordering it, and how question words work alongside it.
A Japanese question is a statement with か on the end. Nothing moves.
学生ですか。
Gakusei desu ka.
Are you a student?
行きますか。
Ikimasu ka.
Are you going?
Compare English, which inverts the verb and sometimes borrows do from nowhere. Japanese appends one syllable and stops.
Written with a full stop
か already marks the question, so the question mark is redundant and formal writing uses 。 instead. In casual writing ？ is common, and after a plain form it is doing real work — see below.
Question words stay in place
Who, what, where do not move to the front. They sit where the answer would sit.
何を食べますか。
Nani o tabemasu ka.
What will you eat?
どこに行きますか。
Doko ni ikimasu ka.
Where are you going?
Read the second literally: where to go? — the question word takes the slot and the particle its answer would take. Answering is then a matter of substitution.
In casual speech か often disappears
Among friends the question is carried by rising intonation alone, and か can sound brusque after a plain form.
行く？
Iku?
Going?
This is where the question mark earns its place: without か and without intonation on the page, nothing else marks it.
学生です？
学生ですか。
Rising intonation stands in for か in casual speech only. After です or ます the particle is expected, and leaving it off sounds unfinished rather than relaxed.