Learn Hardcore Norwegian: Han ligner på sin far.

Both are correct. Many learners find ligner på easier to remember, because it behaves like a verb + preposition unit, similar to English “look like”.

Does på here literally mean “on”?

Literally, på often corresponds to “on”, “in”, or “at”, but in this sentence it does not have a clear, separate meaning.

With ligner (likner) it is best to think of ligner på as a fixed combination meaning “to look like / to resemble”. The på is required by usage, not by a literal meaning.

What is the difference between sin far and hans far?

This is a very important distinction in Norwegian:

sin / sitt / sine = reflexive possessive → refers back to the subject of the clause.
hans = his (someone else’s), not necessarily the subject.

So:

Han ligner på sin far.
= He resembles *his own father.*
Han ligner på hans far.
= He resembles *his (some other man’s) father.
(For example: *He resembles Peter’s father.)

In your sentence, sin tells us that the father belongs to han (the subject).

Could you also say Han ligner faren sin? Is there any difference from sin far?

Yes, you can say both:

Han ligner på sin far.
Han ligner (på) faren sin.

Differences:

sin far = indefinite (far = father)
faren sin = definite (faren = the father)

In practice, both usually mean “his father” and are both normal.
Many people actually prefer faren sin in everyday speech:

Han ligner faren sin. – Very natural.
Han ligner på faren sin. – Also very natural.

The meaning is the same in most contexts.

Can I leave out sin and just say Han ligner på faren?

Grammatically, yes:

Han ligner på faren.

This means “He resembles the father.” Which father? That depends on context:

If the context is clearly about his own father, listeners will probably understand it that way.
Without sin, you lose the explicit link to the subject. It could also mean some other father already known in the conversation.

Using sin (or hans) makes the relationship clear, so for learners it is safer to include it:

Han ligner på sin far. – He looks like his (own) father.

Is ligner (or likner) a reflexive verb because the sentence uses sin?

No. ligner / likner is not a reflexive verb. It is just a normal transitive verb:

å ligne (likne) (på) noen – to resemble someone.

The reflexive element here is the possessive pronoun sin, not the verb.
Sin is reflexive because it refers back to the subject han:

Subject: Han
Possessive referring back to the subject: sin
Object: far

How do the reflexive possessives sin / sitt / sine work in general?

They agree with the noun they describe, not with the owner:

sin – with masculine or feminine singular nouns
- sin far (his/her own father)
- sin mor (his/her own mother)
sitt – with neuter singular nouns
- sitt barn (his/her own child)
sine – with plural nouns
- sine foreldre (his/her own parents)

All of these refer back to the subject of the clause:

Hun elsker sin far. – She loves her own father.
De besøker sine foreldre. – They visit their own parents.

If you use hans / hennes / deres instead, you are talking about someone else’s X, not the subject’s.

How would you say this in the past or future?

The verb å ligne / å likne is regular.

Present:
- Han ligner på sin far. – He resembles his father.
Past (preterite):
Both spellings are accepted in Bokmål:
- Han lignet på sin far.
- Han liknet på sin far.
  – He resembled / looked like his father.
Present perfect:
- Han har lignet på sin far.
- Han har liknet på sin far.
Future:
Usually formed with skal or kommer til å:
- Han skal ligne på sin far. (more like “he is going to / is supposed to resemble his father”)
- Han kommer til å ligne på sin far. (he will end up resembling his father)

Is there a difference between ligner and er lik?

Both can express similarity, but they are used a bit differently:

å ligne (likne) (på) = to resemble, to look like
- Han ligner på sin far. – He looks like his father.
å være lik = to be like, to be similar
- Han er lik faren sin. – He is like his father.

In many contexts they overlap in meaning, but:

ligner på often emphasizes appearance.
er lik can be about appearance or other qualities (personality, behavior) and is also used in maths:
- 2 + 2 er lik 4. – 2 + 2 equals 4.

Are there other common ways to say “He looks like his father” in Norwegian?

Yes, some very common alternatives:

Han ligner (på) faren sin. – He resembles his father.
Han er lik faren sin. – He is like his father.
Han ser ut som faren sin. – He looks like his father (visually focused).
Han er helt lik faren sin. – He is exactly like his father.

All of these are natural; ligner (på) and ser ut som are very frequent in everyday speech.

What about word order – can I move på sin far to the front?

Normal, neutral word order:

Han ligner på sin far.

You can move the prepositional phrase for emphasis or style:

På sin far ligner han.

This is grammatically correct but sounds more poetic, literary, or strongly emphatic. In everyday speech, you usually keep the order:

Subjekt – verb – resten:
Han ligner på sin far.

You cannot place på after the noun; på must come before sin far:

❌ Han ligner sin far på. – Incorrect.

How do you pronounce the words ligner på sin far?

Approximate pronunciation in a standard eastern accent:

ligner – roughly like “LEENG-ner”
- li as in English “lean” (but shorter),
- -g- is often soft or hardly heard,
- -ner as in “nerd” without the d.
på – like “paw” (a long o sound).
sin – like English “seen”, but shorter.
far – similar to English “far”, with a long a.

Spoken together, Han ligner på sin far flows as one rhythm group, with the main stress on ligner and far.

Can ligner på be used only for people, or also for things?

You can use ligner (på) for both people and things:

Hun ligner på moren sin. – She looks like her mother.
Dette huset ligner på huset vårt. – This house looks like our house.
Vinen ligner på den vi drakk i fjor. – The wine is similar to the one we drank last year.

So ligner på = resembles / is similar to, for people, animals, objects, even situations.