Learn Hardcore Hausa: Ni ina aiki yau duk da gajiya. - I am working today despite being tired.

Ni is an independent pronoun (like saying “me / I myself”).
ina is a subject pronoun + aspect marker meaning roughly “I am … (doing)”.

In Ni ina aiki yau duk da gajiya, the Ni adds emphasis or contrast:

Ina aiki yau duk da gajiya.
= I’m working today despite being tired. (neutral)
Ni ina aiki yau duk da gajiya.
= Me, I’m working today despite being tired. (e.g. maybe others are not)

So it’s not redundant; the double “I” is how Hausa shows focus/emphasis on the subject.

You can usually drop Ni if you don’t want that emphasis:
Ina aiki yau duk da gajiya. ✅

What exactly does ina mean here? Is it just “am”?

ina combines subject and aspect:

in- = 1st person singular subject (I)
-a = part of the imperfective/progressive form

Functionally, ina means something like “I am (in the process of)” and is used with a verb or verbal noun:

ina aiki = I am working / I work (right now / generally)
ina karatu = I am studying / reading
ina tafiya = I am going / traveling

So in this sentence:

ina aiki = “I am working” (progressive, ongoing or present-time activity)

Is aiki a verb (“to work”) or a noun (“work”)?

aiki is grammatically a noun meaning “work, job, task”.

But Hausa very often uses nouns in verb-like structures with aspect pronouns like ina:

ina aiki = literally “I am (at/in) work” → I am working
suna bacci = “they are sleep” → they are sleeping
muna wasa = “we are play” → we are playing

So although aiki is a noun, the construction ina + [verbal noun] is translated as an English verb phrase “I am working”.

Could the sentence just be Ina aiki yau duk da gajiya without Ni?

Yes.

Ni ina aiki yau duk da gajiya.
Ina aiki yau duk da gajiya.

Both are correct and mean essentially the same thing:

I am working today despite being tired.

The version with Ni adds extra emphasis on “I”:

Maybe others are resting but you are working.
Or you want to highlight your effort: “As for me, I’m working today, even though I’m tired.”

Without Ni, it’s just a plain, neutral statement.

What does duk da mean, and how is it used?

duk da is a common Hausa expression meaning roughly:

“despite”
“in spite of”
“even though” (when expanded)

In this sentence:

duk da gajiya = despite (the) tiredness / despite being tired

Typical patterns:

duk da + noun
- duk da gajiya – despite tiredness
- duk da ruwan sama – despite the rain
duk da cewa + clause
- duk da cewa na gaji – even though I got tired
- duk da cewa ba ni da kudi – although I don’t have money

So duk da gajiya is a short, compact way to say “even though I’m tired / in spite of being tired.”

Why is it gajiya and not something like na gaji (“I’m tired”)?

Because of duk da.

With duk da, Hausa often uses a noun phrase, not a full clause:

duk da gajiya
= despite tiredness (noun)
duk da zafi
= despite the heat

If you wanted a full clause, you could say:

duk da cewa na gaji
= even though I am tired / I have become tired

But in everyday speech duk da + noun is very natural and concise:

duk da gajiya = despite (my) tiredness

Where does yau (“today”) usually go? Could I say Yau ni ina aiki duk da gajiya?

yau is flexible and can appear in several positions. All of these are acceptable, with slightly different emphasis:

Ni ina aiki yau duk da gajiya.
Ina aiki yau duk da gajiya.
Yau ina aiki duk da gajiya.
Yau ni ina aiki duk da gajiya.

Differences:

Putting yau at the beginning (e.g. Yau ina aiki…) emphasizes “today”:
- Today, I’m working, despite being tired.
Keeping yau after the verb phrase (e.g. Ina aiki yau…) is more neutral.

Your version Yau ni ina aiki duk da gajiya is fine and sounds like:
“Today, me, I’m working despite being tired.” – with emphasis on both today and I.

Is there any verb like “to be” missing here, or is ne/ce needed?

No linking verb is missing, and ne/ce is not needed in this sentence.

ina already functions as “I am … (doing)” in this context.
aiki is the activity you are doing: working.

ne/ce is used in other contexts, for example:

Ni ma’aikaci ne. – I am a worker.
Wannan mota ce. – This is a car.

But in Ni ina aiki yau duk da gajiya, the structure is [subject + progressive] + [activity], and it does not take ne/ce.

How would I say “I’m working today even though I’m NOT tired”?

You can keep the same structure and change the duk da phrase:

Ni ina aiki yau duk da cewa ban gaji ba.

Breakdown:

Ni ina aiki yau – I’m working today
duk da cewa – even though / despite the fact that
ban gaji ba – I’m not tired (negative perfective “I didn’t get tired” → “I’m not tired” in context)

You could also drop Ni if you don’t need emphasis:

Ina aiki yau duk da cewa ban gaji ba.

How would I turn this into a question like “Are you working today despite being tired?”

Change the subject form and use a questioning intonation (or add ne? / ko?):

Kana aiki yau duk da gajiya?
= Are you working today despite being tired?

Details:

kana = you (m.sg) are (progressive)
kina = you (f.sg) are
kuna = you (pl) are

So:

Kana aiki yau duk da gajiya? – to a man
Kina aiki yau duk da gajiya? – to a woman
Kuna aiki yau duk da gajiya? – to more than one person

You can also add ne? at the end for extra clarity as a yes/no question, though intonation alone is usually enough.

Is this sentence formal or informal? Would it sound natural in everyday conversation?

The sentence is informal, natural, everyday Hausa.

Ni ina aiki yau duk da gajiya is exactly the sort of thing you could say to:

a friend on the phone
a colleague
a family member

It’s not slang, and it’s not especially formal. It’s standard, conversational Hausa.