Nei, ég veit ekki.

• Nei = No
• ég = I
• veit = know / do know (the present-tense form of vita)
• ekki = not

So the sentence is built very literally as:

No, I know not.

That word-for-word structure is normal in Icelandic.

Vita is the infinitive, meaning to know.

In the sentence, you need the conjugated form, because the subject is ég (I). The correct present-tense form is:

• ég veit = I know

A few present-tense forms of vita are:

• ég veit = I know
• þú veist = you know
• hann/hún/það veit = he/she/it knows
• við vitum = we know
• þið vitið = you know
• þeir/þær/þau vita = they know

So veit is simply the correct form for ég.

In a normal Icelandic main clause, ekki usually comes after the finite verb.

So:

• Ég veit ekki. = correct, natural

Not:

• Ég ekki veit. = not normal Icelandic

This is one of the basic word-order patterns learners need to get used to. English uses do not know, but Icelandic does not need do. It just puts the negation after the verb:

• ég veit ekki = I do not know

They are both negative, but they do different jobs.

• nei = no, used as a reply or discourse word
• ekki = not, used inside the sentence to negate the verb

So in:

Nei, ég veit ekki.

• Nei answers the other person first: No
• ekki makes the sentence negative: I do not know

You cannot normally swap them.

This is a very common learner question, because English know covers several ideas, but Icelandic splits them up.

Here, vita is used because it means to know a fact / to know information.

Compare:

• Ég veit það. = I know that.
• Ég kann að synda. = I know how to swim.
• Ég þekki hann. = I know him / I am acquainted with him.

So:

• vita = know a fact, know information
• kunna = know how, be able to, sometimes know by heart
• þekkja = know a person/place, be familiar with

In Ég veit ekki, the speaker is saying they do not know the answer or information, so vita is the right verb.

Yes. Ég veit það ekki is very common and natural.

It literally includes það (it/that):

• Ég veit ekki. = I don’t know.
• Ég veit það ekki. = I don’t know it / I don’t know that.

In many situations, both are fine. The version with það can sound a little more like everyday spoken language, especially when referring to a specific thing that was just mentioned.

So if someone asks a question, you may hear both:

• Ég veit ekki.
• Ég veit það ekki.

In careful standard Icelandic, the full sentence is:

Ég veit ekki.

But in casual speech, texting, and informal conversation, people do sometimes say:

Veit ekki.

That is similar to English dropping words in casual speech, like Don’t know.

So:

• Ég veit ekki. = full, standard form
• Veit ekki. = casual, shortened form

As a learner, it is safest to learn and use the full form first.

A rough learner-friendly pronunciation is:

Nay, yehg vate EHK-ki

A few notes:

• Nei sounds roughly like nay
• ég begins with a y sound, something like yehg
• veit sounds roughly like vate or vayt
• ekki has a special Icelandic sound in the middle; learners often approximate it as EHK-ki

The most difficult word here is often ekki, because kk in Icelandic is not pronounced exactly like English kk. It has a breathy / preaspirated quality.

Ég means I.

Two things often surprise English speakers:

• It is not capitalized in the middle of a sentence.
  Icelandic does not capitalize its word for I the way English does.
• The accent in é matters. It is part of the spelling and affects pronunciation.

So:

• Ég veit ekki. = correct
• eg veit ekki = not correct standard spelling

It is neutral and very common.

Nei, ég veit ekki. works in:

• everyday conversation
• class
• work
• polite situations

It is not rude by itself. If you want to sound softer or more polite, you can add something like:

• Því miður, ég veit það ekki. = Unfortunately / Sorry, I don’t know.

But the basic sentence is perfectly normal and polite in most contexts.

The comma shows a small pause between the reply word and the full sentence.

• Nei, ég veit ekki.

This is similar to English punctuation in sentences like:

• No, I don’t know.

So Nei is functioning as a separate response word, and the comma helps show that.

The normal, neutral order is:

Ég veit ekki.

That is the best version for learners to use.

You may sometimes see changed word order for emphasis or style, but those are not the basic pattern. In ordinary speech, stick with:

• Nei, ég veit ekki.

That will sound natural and correct.

No. Icelandic does not use an extra helping verb like English do in this kind of negative sentence.

English:

• I do not know

Icelandic:

• Ég veit ekki

So the negative is made simply by using the verb plus ekki. There is no equivalent of do to insert.