Ég skil ekki neitt.

A rough English-friendly pronunciation is:

yeg skeel EH-kih nayht

A few helpful notes:

• Ég starts with a y sound.
• skil has a long i sound, closer to skeel than skill.
• In ekki, the kk is not quite like English kk; it has a breathy, slightly hk-like feel.
• In neitt, the tt is often pronounced more like ht than a plain English t.

You do not need to get every sound perfect right away; this sentence is very common and will still be understood if your pronunciation is approximate.

No. Icelandic does not capitalize ég just because it means I.

It is capitalized here only because it is the first word of the sentence. In the middle of a sentence, it would normally be written ég, not Ég.

Skil is the 1st person singular present form of the verb skilja, meaning to understand.

So:

• ég skil = I understand
• þú skilur = you understand
• hann/hún/það skilur = he/she/it understands

That is why you get Ég skil, not Ég skilur.

Because that is the normal word order in a simple Icelandic main clause.

In a basic statement, Icelandic usually goes:

subject + finite verb + ekki + other elements

So:

• Ég skil ekki neitt

not

• Ég ekki skil neitt

This is one of the patterns English speakers need to get used to, because Icelandic places ekki differently from English not in some structures.

Yes, from an English point of view it can look like a double negative, but in Icelandic this is completely normal.

ekki = not
neitt = anything

Together, ekki neitt means not anything or nothing.

So Icelandic allows this kind of negative combination in standard language. It is not a mistake.

Neitt is the neuter singular form of neinn, which often means any in negative contexts, questions, and similar situations.

Here it means anything.

It is also functioning as the direct object of skil, so it is in the accusative. The form neitt is the neuter singular nominative/accusative form.

Why neuter? Because there is no specific noun after it. When Icelandic uses this kind of pronoun by itself, neuter singular is very common.

Yes. Ég skil ekkert is very natural and means basically the same thing.

Both are common:

• Ég skil ekki neitt
• Ég skil ekkert

A rough difference is:

• ekki neitt can feel a little more explicit or emphatic
• ekkert is shorter and very idiomatic

In everyday speech, either one is fine.

Yes. Neitt can also appear in places where English uses anything, especially in questions and conditions.

For example:

• Sérðu neitt? = Do you see anything?
• Ef þú þarft neitt, láttu mig vita. = If you need anything, let me know.

So neitt is not limited to negative sentences, but it commonly appears in them.

Then the word based on neinn has to agree with the noun in gender, number, and case.

For example:

• Ég skil ekki neina íslensku. = I don't understand any Icelandic.

Here íslenska is feminine singular, so you use neina, not neitt.

That is an important pattern:

• neitt when the pronoun stands alone
• a matching form such as neina, engan, engin, etc. when a noun follows