Learn Hardcore Latin: Mater rogat filiam: "Quid nunc facis in cubiculo?" - Mother asks her daughter: "What are you doing now in the bedroom?"

So mater rogat filiam literally means the mother asks the daughter.
If it were filia (nominative), it would mean the daughter is the one doing the action, which would change the meaning to the daughter asks.

Could you also say rogat filiam quid faciat? What is the difference?

Yes, you can, but it changes the structure:

mater rogat filiam: "Quid nunc facis in cubiculo?"
= The mother asks her daughter: "What are you doing...?" (direct speech)
mater filiam rogat quid nunc faciat in cubiculo
= The mother asks her daughter what she is doing... (indirect question, in reported speech)

In direct speech, you quote the exact words, so you use normal verb forms: facis.

In an indirect question, Latin uses the subjunctive: faciat instead of facis.

Why is there no word for you in quid nunc facis?

In Latin, the subject pronoun is usually dropped, because the verb ending tells you who is doing the action.

facis = you (singular) do / are doing
The ending -s tells you it’s you.

You could say tu quid nunc facis, but that would emphasize you (like: what are *you doing now?*), and is not normally necessary.

Why is facis translated as are you doing, not simply you do?

Latin has only one present tense, and it covers both:

you do (simple present)
you are doing (present continuous)

So facis can mean you do or you are doing, depending on context.
Here, because it’s a question about what is happening right now (nunc), English naturally uses are you doing.

Why is quid used, and not quod?

quid and quod are different words:

quid = what? (interrogative pronoun, asking a question)
quod = which / that / because, depending on context, but not a standalone question word here.

In a direct question like Quid nunc facis?, Latin always uses quid for what?.
Quod would be wrong in this context.

Why is in cubiculo at the end? Could it come earlier in the sentence?

Latin word order is fairly flexible. In cubiculo could go in several places:

Quid nunc facis in cubiculo?
Quid in cubiculo nunc facis?
In cubiculo quid nunc facis?

All of these are possible. Latin often puts prepositional phrases (like in cubiculo) at or near the end, but that’s a tendency, not a strict rule.

The meaning is determined more by endings (-is, -o, etc.) than by strict word order, unlike English.

Why is it in cubiculo and not in cubiculu or something else?

cubiculum is a neuter second-declension noun:

Nominative singular: cubiculum (subject: the bedroom)
Ablative singular: cubiculo (after in = in the bedroom)

After in:

in
- accusative = motion into: in cubiculum (into the bedroom)
in
- ablative = location in: in cubiculo (in the bedroom)

Here, the mother is asking about what is happening inside the bedroom, not movement into it, so Latin uses in + ablative → in cubiculo.

Is in cubiculo like a “locative case”? I heard Latin has that.

For most nouns, Latin does not use a special locative form; it uses the ablative with in instead:

in cubiculo = in the bedroom (ablative with in)

The true locative case survives only with:

Names of cities, small islands: Romae (in Rome), Athenis (in Athens)
A few common nouns like domi (at home), ruri (in the countryside)

So cubiculo here is just a regular ablative after in.

Why isn’t there a -ne on facis to show that it’s a question?

Latin can mark questions in several ways:

Question word (interrogative)
If you use quid, quis, ubi, quando, cur, quomodo, etc., it’s clearly a question. No -ne is needed.
→ Quid nunc facis?
-ne attached to the verb
Used when there is no other question word:
→ Facisne hoc? (Are you doing this?)

Since this sentence already starts with quid (what?), there is no need for -ne on facis.

Why is there a colon after filiam?

The colon is a modern punctuation convention used to introduce direct speech in printed Latin, similar to English.

Classical Latin manuscripts did not use colons and quotation marks in the modern way. Today, editors write things like:

mater rogat filiam: Quid nunc facis…?

Or sometimes:

mater filiam rogat: "Quid nunc facis in cubiculo?"

It’s just a typographical way to show: these are the exact words spoken.

Why do we say mater rogat filiam, and not mater rogat filiae?

The verb rogo can work in two patterns:

rogo + accusative person + accusative thing (to ask someone something)
- matrem rogo consilium = I ask my mother for advice.
- Person: matrem (acc.)
- Thing: consilium (acc.)
rogo + accusative person + de + ablative thing
- matrem rogo de consilio = I ask my mother about the plan.

In your sentence, filiam is just the person being asked (direct object), so it’s in the accusative.
A dative filiae would be wrong here with rogat in classical usage.

Is mater the subject because it ends in -er?

Not because of -er, but because of its case ending.

mater = nominative singular (subject form of mater, matris – mother)
The nominative case marks the subject of the verb.

The fact that it ends in -er is just the shape this particular word happens to have. Many other nominatives end in -a, -us, -or, etc. Case, not spelling alone, tells you the function.

Could the order be filiam rogat mater? Would that change the meaning?

Yes, filiam rogat mater is grammatically correct and has the same basic meaning:

filiam = accusative, so it must be the object (the one being asked)
mater = nominative, so it’s the subject (the one asking)

Latin listeners/readers rely on endings, not strict word order, to know who is doing what.
Changing the order might give emphasis (for example, starting with filiam could stress the daughter a bit more), but it does not reverse the roles.

Could the mother say Quid nunc agis in cubiculo? instead of facis? Is there a difference?

Yes, agis is possible. The nuance is:

facere = to do, make, perform (very general)
agere = to do, act, be up to something, be busy with something

In practice, Quid nunc facis? and Quid nunc agis? often both mean What are you doing now?

Some teachers prefer quid agis? for How are you?
In a physical/practical sense (what are you up to in your room?), facis is very natural.