Jeg ser nogen i haven.

Ser is the present tense of at se (to see).
It covers both:

• I see someone in the garden.
• I am seeing someone in the garden.

Danish normally doesn’t use a special continuous form (am seeing); ser by itself is enough for both meanings, unless you add extra words like lige nu (right now) for emphasis.

These are all “some/any”-words, but used in different situations:

• nogen

  • Basic meaning: someone / anyone (person, singular, unspecified)
  • Jeg ser nogen i haven. = I see someone in the garden.
  • After ikke (not), it usually means anyone:
    
    • Jeg ser ikke nogen. = I don’t see anyone.

• noget

  • Neuter / “thing” / mass: something / anything / some (uncountable)
  • Jeg ser noget i haven. = I see something in the garden.

• nogle

  • Plural, countable: some (people or things)
  • Jeg ser nogle børn i haven. = I see some children in the garden.

Danish usually attaches the definite article (the) to the end of the noun:

• have = garden
• haven = the garden

So i haven literally is in garden-the, which corresponds to in the garden in English.
You don’t say i den have in normal speech; you say i haven.

i generally means in / inside, while på often means on / at, but usage is idiomatic and must often be memorized.

For have (garden):

• Natural: i haven = in the garden
• på haven would be wrong in standard Danish.

Some place words take i, others på:

• i byen = in town
• på arbejdet = at work
• i skoven = in the forest
• på landet = in the countryside

So here i haven is the correct and idiomatic choice.

The neutral word order is:

• Subject – Verb – (Object) – (Place):
  Jeg ser nogen i haven.

You can move i haven to the front for emphasis on the place:

• I haven ser jeg nogen. = In the garden, I see someone.

But the verb must stay in second position in main clauses (the V2 rule), so:

• ✔ I haven ser jeg nogen.
• ✘ I haven jeg ser nogen.

Jeg ser i haven nogen is technically possible but sounds marked/unnatural here; a Dane would usually keep nogen before i haven or put i haven first.

In a positive sentence like:

• Jeg ser nogen i haven.

the natural translation is someone.

In negative or question contexts, nogen often corresponds to anyone:

• Jeg ser ikke nogen i haven. = I don’t see anyone in the garden.
• Ser du nogen i haven? = Do you see anyone in the garden?

So the word nogen itself is flexible; the meaning (someone vs anyone) is determined by context (positive vs negative/question).

Jeg is the subject form (I), and mig is the object form (me).

• Jeg ser nogen i haven. = I see someone in the garden.
  
  • Jeg is doing the seeing → subject.

If you were the one being seen:

• Nogen ser mig i haven. = Someone sees me in the garden.
  
  • mig is the object (the one being seen).

So use jeg as the subject of the verb, and mig when it’s the object.

Approximate pronunciation in simple English-like terms (standard Danish):

• Jeg ≈ yai (like English eye with a soft y at the start)
• ser ≈ seh or sehr (the r is often soft, not strongly rolled)
• nogen ≈ noon or no-en (many Danes reduce the middle vowel; you may hear something like noon with a soft n at the end)
• i ≈ ee (as in see)
• haven ≈ HAW-en or HAY-un, with a soft v/w sound and often a very soft or almost swallowed -n

Spoken quickly, the sentence can sound like:
“Yai sehr noon i HAW-en” (very approximate).

In Jeg ser nogen i haven:

• nogen is understood as one, unspecified person → someone.

For more than one, you normally use nogle:

• Jeg ser nogle personer i haven. = I see some people in the garden.

So in this sentence, a Dane will understand nogen as singular and personal.

No. Nogen already functions as an indefinite pronoun:

• nogen = someone / anyone

You don’t add another article:

• ✘ en nogen – ungrammatical
• ✔ nogen – correct

If you want to specify more, you add a noun, but without an article in this structure:

• nogen person = some person / someone
• en person = a person
• den person = that/the person

Danish yes–no questions use verb–subject inversion:

• Statement: Du ser nogen i haven. = You see someone in the garden.
• Question: Ser du nogen i haven? = Do you see someone/anyone in the garden?

Note:

• The verb ser moves in front of the subject du.
• The rest of the sentence stays in the same order.

• at se = to see (perceive with your eyes, often more neutral)

  • Jeg ser nogen i haven. = I see someone in the garden.

• at kigge (på) = to look (at), to watch (an active action, directing your eyes)

  • Jeg kigger på nogen i haven. = I’m looking at someone in the garden.

You must include på with kigge when there is an object:

• ✘ Jeg kigger nogen i haven. – wrong
• ✔ Jeg kigger på nogen i haven. – correct

In your original sentence, ser is the right verb.