Boken ligger oppå bordet.

Because boken is the definite form of bok.

• bok = a book
• boken = the book

In Norwegian, definiteness is often shown by adding an ending to the noun rather than using a separate word like the.

For this noun:

• en bok = a book
• boken = the book

So Boken ligger oppå bordet means the book is being talked about, not just any book.

For the same reason: bordet is the definite form of bord.

• et bord = a table
• bordet = the table

So both nouns in the sentence are definite:

• boken = the book
• bordet = the table

Norwegian often attaches definiteness directly to the noun:

• en/et for a/an
• noun ending for the

Ligger is the present tense of ligge, which usually means lies, is lying, or is located in a lying/horizontal position.

In Norwegian, you often do not use er where English simply says is for physical position. Norwegian prefers more specific position verbs:

• ligge = lie / be lying
• stå = stand / be standing
• sitte = sit / be sitting

So a book on a table is naturally said to lie there:

• Boken ligger oppå bordet.

Using er would sound less natural here because Norwegian likes to describe how something is positioned.

Because Norwegian often chooses a verb based on the object's typical physical position.

A book on a table is usually thought of as being flat or horizontal, so Norwegian uses ligge.

Compare:

• Boken ligger på bordet. = The book is lying on the table.
• Flasken står på bordet. = The bottle is standing on the table.
• Bildet henger på veggen. = The picture is hanging on the wall.

This is one of the big differences from English: English often just says is, but Norwegian often chooses a position verb.

Oppå means something like on top of and emphasizes that one thing is physically resting on the upper surface of another.

• på = on
• oppå = on top of

In many everyday situations, both can work:

• Boken ligger på bordet.
• Boken ligger oppå bordet.

But oppå gives a slightly stronger sense of right on top of the surface.

So:

• på bordet can simply mean on the table
• oppå bordet stresses on top of the table

In this sentence, it is normally written as one word: oppå.

That is the standard form when used as the preposition meaning on top of.

So this is correct:

• Boken ligger oppå bordet.

Learners sometimes want to separate it because it looks like opp + på, but in normal modern spelling here, oppå is written as one word.

This is the normal word order for a simple statement:

• Boken = subject
• ligger = verb
• oppå bordet = place expression

So the structure is:

Subject + Verb + Place

That is completely normal in Norwegian:

• Boken ligger oppå bordet.
• Mannen sitter i stolen.
• Bilen står utenfor huset.

Norwegian main clauses usually place the finite verb in the second position, and this sentence follows that pattern naturally.

Yes, grammatically you can, but the meaning changes.

• En bok ligger oppå bordet. = A book is lying on top of the table.
• Boken ligger oppå bordet. = The book is lying on top of the table.

So the difference is definiteness:

• en bok = a book, not specific
• boken = the book, specific

Likewise:

• et bord = a table
• bordet = the table

The basic forms are:

• bok = book
• ligge = to lie
• oppå = on top of
• bord = table

The sentence uses inflected forms:

• boken = definite singular of bok
• ligger = present tense of ligge
• bordet = definite singular of bord

So if you were looking the words up in a dictionary, you would usually search for:

• bok
• ligge
• oppå
• bord

This is a matter of grammatical gender, which has to be learned with the noun.

• en bok = a book
• et bord = a table

These genders affect the indefinite article and the definite ending:

For en words:

• en bok
• boken

For et words:

• et bord
• bordet

So the sentence gives you a useful pattern:

• bok is a common-gender noun
• bord is a neuter noun

A careful approximate pronunciation is:

BOO-ken LIG-ger OP-poh BOOR-det

A few helpful notes:

• boken: the o is long, roughly like the vowel in boot, though not exactly the same
• ligger: the gg is pronounced like a hard g sound; the first syllable is stressed
• oppå: stress usually falls on the last part, -på
• bordet: the r may sound different depending on dialect

If you are learning Bokmål pronunciation, it is best to listen to native recordings, since Norwegian pronunciation varies a lot by region.

Yes. With ligger, Norwegian can express both physical position and location.

In this sentence, it means the book is located there, but it still uses the position verb that fits the object’s orientation. So ligger does two jobs at once:

• it tells you where the book is
• it suggests the book is in a lying/flat position

That is very natural in Norwegian. English often just says The book is on the table, but Norwegian prefers the more specific Boken ligger oppå bordet or Boken ligger på bordet.