Eierskiftet skjer ikke uten at salgsmeldingen er signert.

Eierskiftet means the change of ownership or the transfer of ownership.

The base noun is et eierskifte = a change of ownership.
When it becomes definite, it takes the ending -et:

• et eierskifte = a change of ownership
• eierskiftet = the change of ownership

This is very common in Norwegian: the definite article is usually added to the end of the noun instead of being a separate word like the in English.

Because it is also in the definite form: the sales notification / the sale report.

The base noun is en salgsmelding.
In definite form:

• en salgsmelding = a sales notification
• salgsmeldingen = the sales notification

So this sentence has two definite nouns:

• eierskiftet = the ownership transfer
• salgsmeldingen = the sales notification

That makes sense in an official or administrative context, where both refer to specific known documents or processes.

Skjer is the present tense of å skje, which means to happen, to take place, or to occur.

So:

• skjer = happens / takes place / occurs

In this sentence, Eierskiftet skjer ikke ... means something like:

• The transfer of ownership does not take place ...
• The ownership change does not happen ...

This verb is often used in formal or neutral statements about events and processes.

Because in a normal Norwegian main clause, the finite verb usually comes in the second position, and ikke typically comes after that verb.

So:

• Eierskiftet = first element
• skjer = finite verb in second position
• ikke = negation after the verb

That gives:

• Eierskiftet skjer ikke ...

This is standard Norwegian word order. Compare:

• Han kommer ikke. = He is not coming.
• Det gjelder ikke. = That does not apply.

Uten at means without ... followed by a full clause.

Here it introduces the condition that has not been met:

• uten at salgsmeldingen er signert
  = without the sales notification being signed

A very natural English translation is often:

• unless the sales notification has been signed
• without the sales notification being signed

So uten at is used when what follows has its own subject and verb:

• uten at han vet det = without him knowing it
• uten at de kom = without them coming

If there is no full clause after uten, Norwegian often just uses uten by itself:

• uten sukker = without sugar

Because at introduces a subordinate clause, similar to that in English, although it is often not translated directly.

In uten at salgsmeldingen er signert, the part after at is a full clause:

• salgsmeldingen = subject
• er signert = verb phrase

So uten at is a set pattern meaning without it being the case that ... or more naturally without ...

You should think of uten at as a common combination rather than translating each word separately every time.

Because er signert describes the document as being in a signed state: is signed / has been signed.

This is a passive/resultative type of expression:

• salgsmeldingen er signert = the sales notification is signed / has been signed

By contrast, har signert usually means has signed and normally needs a person as subject:

• Han har signert salgsmeldingen. = He has signed the sales notification.

So:

• salgsmeldingen er signert focuses on the document
• han har signert salgsmeldingen focuses on the person who signed it

You can think of it as a past participle used with er.

In practice, this often works very much like an adjective in meaning:

• Dokumentet er signert. = The document is signed.

But it is also closely related to the verb å signere = to sign.

For learners, the most useful way to understand it is:

• er signert = is signed / has been signed

You do not need to force a strict adjective-versus-verb distinction every time, because Norwegian often uses past participles in exactly this kind of way.

Not exactly, but in this sentence unless is a very natural English translation.

The Norwegian structure literally means something like:

• The ownership transfer does not happen without the sales notification being signed.

In idiomatic English, we often prefer:

• The ownership transfer will not take place unless the sales notification is signed.

So the meanings are very close here.
Still, uten at is structurally without + clause, not literally unless.

Because after at, Norwegian uses subordinate clause word order.

In this particular clause there is no ikke, so the order looks similar to English:

• salgsmeldingen = subject
• er = finite verb
• signert = participle

If there were a negation, you would see the subordinate word order more clearly:

• ... uten at salgsmeldingen ikke er signert would be ungrammatical in this meaning
• but compare another subordinate clause:
  • Jeg vet at han ikke kommer. = I know that he is not coming.

In subordinate clauses, ikke normally comes before the finite verb phrase, unlike in main clauses.

Yes, it sounds fairly formal and administrative.

Words like:

• eierskiftet
• salgsmeldingen
• signert

make it sound like something from a government website, form instructions, or an official procedure, especially in contexts such as vehicle registration or property transfer.

A more everyday spoken version might be phrased differently, but this sentence is perfectly natural in official Norwegian.

Yes. A word-for-word translation would be something like:

• The change of ownership does not happen without the sales notification being signed.

But more natural English could be:

• The transfer of ownership will not take place unless the sales notification is signed.
• The ownership transfer cannot be completed until the sales notification has been signed.

The exact best translation depends on context, but the Norwegian sentence itself is clear and standard.

Yes, and that would change the nuance slightly.

• Eierskiftet skjer ikke uten at ... = The transfer does not happen without ...
• Eierskiftet kan ikke skje uten at ... = The transfer cannot happen without ...

The version with kan ikke sounds a bit more explicitly about impossibility or requirement.
The version you were given sounds like a formal statement of procedure: this is simply how the process works.

Both are natural, but the original is a very typical bureaucratic way to phrase it.