ко / шта / где / куда / када / како

To ask open-ended questions in Serbian, place the interrogative word first, followed either by the enclitic cluster (verbal and pronominal clitics) or directly by the verb/subject.

1. Pronouns vs. Adverbs
• ко (who) and шта (what) are interrogative pronouns. When used as subjects, ко triggers masculine singular agreement (e.g., Ко је дошао?) and шта triggers neuter singular agreement (e.g., Шта се догодило?). In other roles, they decline for case:
- Genitive: кога, чега
- Dative: коме / ком (for ко), чему (for шта)
- Accusative: кога (prescriptively used for persons/human beings, though pets and personified animals colloquially appear with ко / кога as well; e.g., Кога чекаш?), шта (used for non-human entities, objects, and abstract concepts; e.g., Шта видиш?, Шта тражиш?)
- Instrumental: ким(е), чим(е). The preposition с (or vocalized са) is used for accompaniment or ingredients: С ким идеш? and С чим је ова пита? are standard canonical forms, though Са ким and Са чим are also widely accepted and frequent in everyday speech (the vocalized form са is strictly mandatory phonotactically before sibilants like с, з, ш, ж, certain heavy consonant clusters, or мном). When asking about an instrument or means, the preposition is omitted entirely (e.g., Чим(е) пишеш?). Note that the optional final -е in ким/киме and чим/чиме is a true movable vowel (покретни вокал).
- Locative: (always with a preposition) (о) коме / ком, (о) чему.
• где (where), куда (where to), када (when), and како (how) are adverbs, meaning they do not decline for case, gender, or person. Note that када and куда often appear in their shorter variant forms кад and куд (due to a movable vowel). In standard Ijekavian Serbian, 'where' is гдје alongside Ekavian где. To ask 'why', standard Serbian uses the interrogative adverb зашто (e.g., Зашто ћутиш?), while што is also very frequently heard in informal speech meaning 'why' or 'how come' (e.g., Што не спаваш?).

2. Manner, State, and Greetings with 'Како'
The adverb како primarily asks about manner or method (e.g., Како правиш ову кафу? — How do you make this coffee?). Crucially, Serbian also uses како to ask about someone's state, health, well-being, or condition (e.g., Како си? — How are you?; Како сте? — How are you? [polite/plural]) as well as idiomatic questions such as names (e.g., Како се зовеш? — What is your name?).

3. 'Где' vs. 'Куда'
Prescriptively, где asks for a static location (e.g., Где живиш?), while куда asks for destination or direction of motion (e.g., Куда путујеш?). In everyday speech, you will often hear где used for motion as well (e.g., Где идеш?), but keeping them distinct is standard practice.

4. 'Шта' vs. Adjectives
Шта stands alone as a noun-pronoun. It cannot modify another noun directly like English 'what car'. To say 'which car' or 'what kind of car', use који or какав instead.

5. Word Order with Clitics
Serbian question words usually occupy the first position in the sentence. Any clitics (auxiliary clitics such as бити forms, future ћу, ћеш, ће..., or conditional forms; pronominal clitics like ми or га; and reflexive се) immediately follow in the second structural position (e.g., Како се зовеш?, Шта му кажеш?, Куда ћеш ићи?). If no clitics are present, a full noun or subject can also come directly after the question word (e.g., Када твој брат долази?).