Na mom krevetu su farmerke i čarape koje sada tražim.

Krevetu is in the locative singular.

The preposition na can take different cases depending on meaning:

• na + locative = location, on / at
• na + accusative = movement toward something, onto / to

So:

• Na mom krevetu su farmerke. = The jeans are on my bed.
• Stavljam farmerke na moj krevet. = I am putting the jeans onto my bed.

Here the sentence describes where the clothes are, so Serbian uses na + locative.

Because mom has to agree with krevetu.

Moj is the basic dictionary form, but adjectives and possessive words change for case, gender, and number.

Since krevetu is:

• masculine
• singular
• locative

the possessive becomes mom:

• moj krevet = my bed
• na mom krevetu = on my bed

You may also hear mojem in some styles:

• na mojem krevetu

Both are correct, but mom is very common and natural.

Because su is a clitic in Serbian.

Clitics are short unstressed words that usually take the second position in the sentence or clause. Forms of biti in the present tense often behave this way:

• sam, si, je, smo, ste, su

So in this sentence:

• Na mom krevetu = first phrase
• su = goes right after that phrase

That is why we get:

• Na mom krevetu su farmerke i čarape...

This is normal Serbian word order.

Serbian usually does not need a separate word for there is / there are in this kind of sentence.

English says:

• There are jeans and socks on my bed.

Serbian simply says:

• Na mom krevetu su farmerke i čarape.

Literally, this is closer to:

• On my bed are jeans and socks.

So Serbian often expresses existence or presence just by using the normal verb to be plus word order.

In Serbian, farmerke is normally a plural-only noun when it means a pair of jeans.

So:

• farmerke su = the jeans are

This is similar to English words like:

• jeans
• pants
• shorts

Even though it refers to one item of clothing, grammatically it is plural.

Examples:

• Ove farmerke su nove. = These jeans are new.
• Gde su moje farmerke? = Where are my jeans?

Because čarape means socks, plural.

The singular is:

• čarapa = sock

The plural is:

• čarape = socks

So the sentence is talking about:

• farmerke = jeans
• čarape = socks

Both nouns are plural, which is why the verb is also plural:

• su

Koje refers to farmerke i čarape.

It introduces the relative clause:

• koje sada tražim = that I am looking for now

So the whole structure is:

• Na mom krevetu su farmerke i čarape
• koje sada tražim

Together:

• On my bed are the jeans and socks that I am looking for now.

In other words, the speaker is looking for those clothes, and they turn out to be on the bed.

Because it has to match the noun phrase it refers to.

Here the antecedent is:

• farmerke i čarape

Both nouns are:

• feminine plural

So the relative pronoun is also plural, and the correct form here is koje.

Also, inside the clause tražim koje, the pronoun is the direct object, so it is in the accusative. For feminine plural, nominative and accusative have the same form here, so you still see koje.

That is why:

• koje sada tražim = which/that I am looking for now

Tražim means I am looking for / I look for.

Serbian verbs usually already show the subject, so the pronoun ja is often omitted.

• tražim = I am looking for
• tražiš = you are looking for
• traži = he/she is looking for

So Serbian does not need to say:

• ... koje ja sada tražim

It can say that, but it is usually unnecessary unless you want emphasis:

• ... koje ja sada tražim = ... that I am looking for now

Without emphasis, tražim alone is enough.

No, Serbian word order is fairly flexible.

These are all possible, with slightly different emphasis:

• koje sada tražim
• koje tražim sada
• koje baš sada tražim

The version in your sentence, koje sada tražim, is very natural. It puts sada in a clear, neutral place inside the relative clause.

In this sentence, the most natural reading is that koje refers to both nouns together:

• farmerke i čarape koje sada tražim

Because the structure groups them as one plural noun phrase.

If a speaker wanted to make it clear that only the socks are being referred to, Serbian would usually restructure the sentence, for example:

• Na mom krevetu su farmerke i čarape koje tražim.
  This can still sound like both, depending on context.

More explicit versions might be:

• Na mom krevetu su farmerke i one čarape koje sada tražim.
• Na mom krevetu su farmerke, a i čarape koje sada tražim.

So in your original sentence, learners should understand koje as referring to the whole phrase farmerke i čarape.

Yes. That is also correct.

• Na mom krevetu su farmerke i čarape... = simple, natural, everyday
• Na mom krevetu se nalaze farmerke i čarape... = a bit more formal or descriptive

The verb nalaziti se means to be located / to be situated.

So both are grammatical, but su is shorter and more common in ordinary speech.

This is a very common and important distinction:

• na krevetu = on the bed
• u krevetu = in bed / in the bed

Examples:

• Farmerke su na krevetu. = The jeans are on the bed.
• Dete je u krevetu. = The child is in bed.

So in your sentence, na mom krevetu clearly means the clothes are lying on top of the bed.