I den lille genbrugsbutik købte jeg et brugt bord, som stadig ser næsten nyt ud.

No. Here I means in. It is capitalized only because it is the first word of the sentence.

So:

• i = in
• I den lille genbrugsbutik = In the small thrift store / second-hand shop

This often catches English speakers because Danish i looks exactly like English I.

Because butik is a common-gender noun in Danish:

• en butik = a shop
• so in the definite phrase it becomes den ... butik

Danish has two grammatical genders:

• common gender: usually takes en / den
• neuter: usually takes et / det

Since genbrugsbutik ends with butik, it keeps the gender of butik, so it is:

• en genbrugsbutik
• den lille genbrugsbutik

Because Danish very often makes compound nouns by writing them as a single word.

Here:

• genbrug = reuse / recycling / second-hand
• butik = shop

So:

• genbrugsbutik = literally something like reuse-shop
• natural English equivalent: thrift store, second-hand shop

A useful rule: in Danish compounds, the last part is the main noun and decides the gender. Since the last part is butik, the whole word is common gender: en genbrugsbutik.

Because Danish follows the V2 rule in main clauses: the finite verb usually comes in the second position.

If the sentence starts with the subject, you get:

• Jeg købte et brugt bord ...

But if you move another element to the front for emphasis, the verb still stays second:

• I den lille genbrugsbutik købte jeg et brugt bord ...

So the pattern is:

1. fronted element: I den lille genbrugsbutik
2. finite verb: købte
3. subject: jeg

This is very common in Danish.

Because bord is a neuter noun:

• et bord = a table

When an adjective comes before an indefinite singular neuter noun, the adjective usually gets -t:

• et nyt bord = a new table
• et brugt bord = a used table

So:

• et because bord is neuter
• brugt because the adjective agrees with a neuter singular noun

Yes. Here brugt is functioning as an adjective meaning used or second-hand.

It comes from the verb bruge = to use, but in this sentence it describes the noun:

• et brugt bord = a used table

So although it originally comes from a verb form, you can treat it here as a normal adjective.

They are related, but they do different jobs.

• brugt describes the table: it is used
• genbrugs- is part of genbrugsbutik, which describes the type of shop: a second-hand / thrift shop

So the sentence says that the speaker bought:

• a used table
• in a second-hand shop

They come from related ideas of using and reusing, but they are not interchangeable.

Because som stadig ser næsten nyt ud is a relative clause, and Danish normally separates that kind of clause with a comma.

The comma marks extra information about bord:

• et brugt bord = the noun
• som stadig ser næsten nyt ud = information describing that noun

So the comma helps show where the description begins.

Here som introduces a relative clause and means something like that, which, or sometimes who, depending on what it refers to.

In this sentence it refers to bord:

• et brugt bord, som stadig ser næsten nyt ud
• a used table that/which still looks almost new

Here som is the subject of the relative clause, because it is the table that looks almost new.

Because it is a subordinate clause, and Danish subordinate clauses often place adverbs like stadig before the finite verb.

So you get:

• som = relative word
• stadig = still
• ser = looks
• næsten nyt ud = almost new

Compare the basic idea:

• main clause style: Det ser stadig nyt ud
• relative clause: ... som stadig ser nyt ud

For English speakers, the main thing to notice is that Danish word order changes between main clauses and subordinate clauses.

Because nyt agrees with bord, which is a neuter noun.

The table is what looks almost new:

• et bord
• therefore nyt

Compare:

• en stol ser ny ud = a chair looks new
• et bord ser nyt ud = a table looks new

So even though nyt comes later in the sentence, it still matches the noun it describes.

Because se ud is a fixed Danish verb expression meaning to look / to appear.

In actual sentences, the parts are often separated:

• Bordet ser nyt ud = The table looks new
• Det ser godt ud = It looks good

So in your sentence:

• ser = finite verb
• ud = particle that belongs with it
• together: ser ud = looks / appears

The adjective or description usually goes between them:

• ser næsten nyt ud
• looks almost new

They fine-tune the description.

• stadig = still
• næsten = almost

So:

• stadig ser næsten nyt ud = still looks almost new

This suggests that even though the table is used, its condition is very good.

Without them, ser nyt ud would simply mean looks new. With stadig and næsten, the sentence sounds more natural and precise.