Learn Hardcore Swahili: Ndiko anakoishi Amina, pembeni ya shule. - That is where Amina lives, beside the school.

Ndiko is an emphatic locative copular form (one of the “nd-” forms). It means “it is there (in that place) that…,” and is used to focus or cleft the location. So the sentence has the sense “It is there that Amina lives, next to the school,” highlighting the place.

Why do I see -ko twice (in ndiko and in anakoishi)?

They agree with each other. In a cleft like this, the locative in the focus part (ndiko) is matched by the same locative relative marker in the verb (-ko- in a-na-ko-ishi). If you change one, you change the other:

Ndipo anapoishi Amina… (specific/definite place: -po/-po)
Ndimo anamoishi Amina… (inside a place: -mo/-mo)
Ndiko anakoishi Amina… (general/unspecified or distant: -ko/-ko)

Could I use ndipo instead of ndiko here?

Yes, and many speakers would prefer it because the place is specific (“next to the school”). So:

More idiomatic for a specific spot: Ndipo anapoishi Amina, pembeni ya shule.
Your sentence with ndiko … anakoishi is still grammatically valid, and some speakers use -ko more broadly.

What exactly is inside the verb anakoishi?

It’s a relative verb form:

a- = subject marker (she/he)
-na- = present tense
-ko- = locative relative marker (“where”)
-ishi = verb root “live” So a-na-ko-ishi ≈ “(she) lives where …,” i.e., “where she lives.”

Why is Amina after the verb instead of before it?

In Swahili the subject is already marked on the verb (a- = she/he), so the noun phrase Amina can come after the verb, especially in relative and focus constructions. You could also say:

Ndiko Amina anakoishi, pembeni ya shule. Both orders are acceptable; the given one is common in cleft sentences.

Do I need the comma before pembeni ya shule?

It’s optional and reflects intonation. Pembeni ya shule is an appositive/afterthought specifying the place. Without a comma is also fine. A non-cleft alternative is simply: Amina anaishi pembeni ya shule.

Why is it pembeni ya shule and not pembeni na shule?

Because pembeni ya X means “beside/at the side of X,” using the possessive connector ya (“the side of”). Other location phrases use different connectors:

karibu na shule = near the school (uses na)
mbele ya shule = in front of the school (uses ya)
nyuma ya shule = behind the school (uses ya)

What’s the difference between pembeni ya, kando ya, and karibu na?

pembeni ya = right at the side/edge of; typically closer and lateral.
kando ya = at/by the side/edge of; often interchangeable with pembeni ya.
karibu na = near/close to (not necessarily exactly at the side). All are natural; nuance is closeness and “side-of” vs. general proximity.

How do -po, -ko, and -mo differ?

They’re locative sets:

-po = a specific/definite, often visible/known spot (“right there/here”).
-ko = a general or more distant/unspecified place (“there, somewhere there”).
-mo = inside/within a place. Match them across the cleft and the relative:
Hapo ndipo anapoishi Amina…
Huko ndiko anakoishi Amina…
Humo ndimo anamoishi Amina…

Can I say the same thing without a cleft/focus structure?

Yes. The straightforward version is:

Amina anaishi pembeni ya shule. You can add a demonstrative if needed:
Amina anaishi pale pembeni ya shule.

Is anakoishi just another way to say anaishi?

No. anaishi = “she lives.” anakoishi is a relative form meaning “where she lives,” which must relate to a head like ndiko/hapo/mahali. In your sentence, ndiko is that head.

Can I include a word like mahali (“place”)?

You can, but it’s usually redundant in a cleft because ndiko already serves as the locative head:

Redundant/formal: Ndiko mahali anakoishi Amina, pembeni ya shule.
More natural: keep mahali only if you drop the cleft: Mahali anakoishi Amina ni pembeni ya shule.

How would this change with a plural subject?

You change the subject marker:

Ndipo wanapoishi watoto, pembeni ya shule. (“That is where the children live, next to the school.”) Here wa- = they (plural), and -po matches ndipo.