Learn Hardcore Croatian: Tko dolazi na ručak danas?

In standard Croatian, tko means “who.” You will hear and see ko in colloquial speech, and it is standard in Serbian and Bosnian, but Croatian prescriptive standard prefers tko in writing and formal speech. Both are widely understood.

What case is tko, and what are the other forms (whom, to whom, with whom)?

Nominative (who?): tko — used for the subject, as in this sentence.
Genitive/Accusative (of whom / whom?): koga
Dative/Locative (to whom / about whom): komu / kome (both are fine)
Instrumental (with whom): s kim
Note the stem change t- → k- in the oblique cases (koga, kome, kim).

Why is the verb singular (dolazi) even if several people might be coming?

With the interrogative tko, the verb is grammatically singular: Tko dolazi…? is correct. Even if the answer is plural (e.g., “Ana i Marko”), you still ask in the singular.

Correct: Tko dolazi na ručak danas?
Incorrect: Tko dolaze…?
Possible fuller question for “who all”: Tko sve dolazi…? (still singular).

What’s the difference between dolaziti and doći, and could I say this in the future or past?

dolaziti (imperfective) focuses on the process/habit; present: dolazi = “is coming/comes.”
doći (perfective) focuses on the completed arrival.
Useful variants:
Future: Tko će doći na ručak danas? (Who will come…?)
Past: Tko je došao na ručak? (Who came…?)

Why is it na ručak and not za ručak or u ručak?

na + Accusative = motion/goal toward an event: na ručak = “to (for) lunch (as an event).”
Example: Idemo na ručak.
za + Accusative = “for (as a purpose/menu).”
Example: Što je za ručak? (What’s for lunch?)
u ručak is not used for this meaning.

What case is ručak here, and why doesn’t it change form?

It’s Accusative singular after na (motion). Masculine inanimate nouns often have the same form in Nominative and Accusative: ručak → ručak.
Contrast with the static location (Locative): na ručku = “at lunch” (I’m at the lunch).

Is the position of danas fixed? Is Tko danas dolazi na ručak? also correct?

Word order is flexible. All of these are fine, with slight differences in emphasis:

Tko danas dolazi na ručak? (very neutral)
Tko dolazi danas na ručak?
Tko dolazi na ručak danas? (mild emphasis on “today” at the end)

How do I pronounce tko and ručak?

tko: pronounce the t; it’s a real cluster: [t-ko].
ručak: each letter sounds; č is like the “ch” in “church”; u is like “oo” in “food”; final k is crisp; Croatian r is tapped/rolled. There are no silent letters.

Can I use koga (whom) instead of tko here?

No. Tko is the subject (“who is coming”). Koga is used for the object:

Subject: Tko dolazi na ručak? (Who is coming?)
Object: Koga zoveš na ručak? (Whom are you inviting to lunch?)

Why are there no articles like “a/the” in the sentence?

Croatian has no articles. Definiteness is understood from context. na ručak simply means “to (for) lunch,” and context clarifies which lunch (e.g., today’s lunch, the one at your place, etc.).

How could I answer this question in Croatian?

Single person: Ana dolazi.
Multiple people: Dolaze Ana i Marko.
Nobody: (short) Nitko. / (full) Nitko ne dolazi.
I don’t know: Ne znam.
Note: negation uses double negative in full sentences (e.g., Nitko ne dolazi).

How do I turn this into a yes/no question like “Is anyone coming to lunch today?”

Use li and netko/itko:

Neutral/expecting yes: Dolazi li netko na ručak danas?
More open/anyone at all: Dolazi li itko na ručak danas?
Both are acceptable; itko often appears in negative or doubtful contexts.

Could I drop danas or move it to the front?

Yes:

Without it: Tko dolazi na ručak? (Who is coming to lunch?)
Fronted: Danas tko dolazi na ručak? is unusual; better: Tko danas dolazi na ručak? or Danas tko dolazi? only in very marked, conversational contexts. Generally keep danas after tko.

How do I ask the same thing for other meals?

Breakfast: Tko dolazi na doručak danas?
Dinner: Tko dolazi na večeru danas?
The pattern na + [meal] stays the same.