Is it possible to ask a question in Esperanto without 'ĉu,' or is this strictly grammatically incorrect? Especially in speech comes to mind, when asking with an inflection.
Yes. Many questions are formed using the interrogative correlatives(kio, kiu, kial etc.). Examples are
- Kial vi ploras? (Why are you crying?)
- Vi faris kion? (You did what?)
It is also possible to construct sentences without ĉu or any of the interrogative correlatives, see Question structure in Esperanto.