Ne znam dobro šivati, ali ovaj šav mogu popraviti.

Yes. Znati can mean both:

• to know a fact: Znam odgovor. = I know the answer.
• to know how to / be able to by learned skill: Znam plivati. = I know how to swim.

So Ne znam dobro šivati means I don’t sew well / I don’t know how to sew well.

After znati in this meaning, Croatian normally uses the infinitive:

• Znam kuhati. = I know how to cook.
• Ne zna voziti. = He/She doesn’t know how to drive.

So:

• šivati = to sew
• šivam = I sew / I am sewing

In this sentence, the speaker is talking about the skill in general, so the infinitive šivati is the natural form.

Dobro is an adverb meaning well.

So:

• Ne znam šivati. = I don’t know how to sew.
• Ne znam dobro šivati. = I don’t know how to sew well.

It modifies the verb phrase, not a noun.

They are related in meaning, but they are different parts of speech:

• šivati = to sew (verb)
• šav = seam / stitch (noun)

So the sentence contrasts the general skill of sewing with one specific thing that can be fixed:

• Ne znam dobro šivati = I’m not good at sewing
• ali ovaj šav mogu popraviti = but I can repair this seam

Because šav is a masculine inanimate noun, and in the accusative singular it has the same form as the nominative.

Here ovaj šav is the direct object of popraviti:

• nominative: ovaj šav
• accusative: ovaj šav

If it were a masculine animate noun, the accusative would look different.

Mogu popraviti means I can repair / I am able to repair. It expresses ability.

• mogu = I can
• popraviti = to repair / to fix

So the speaker is saying:

• I’m not good at sewing in general,
• but I am able to fix this particular seam.

If you said ali ovaj šav popravim, that would not mean the same thing.

This is a matter of aspect.

• popraviti = perfective → to fix something successfully, as a completed act
• popravljati = imperfective → to be fixing, to fix repeatedly, or in a more general/process sense

Here the speaker means a single concrete result: fixing this one seam. So popraviti is the natural choice.

Yes, depending on context. In this sentence, seam is probably the most natural translation, but stitch may also fit in some contexts.

A learner should mainly understand that šav refers to the sewn line or join in fabric.

Yes. Ali is the basic Croatian word for but.

It introduces a contrast:

• Ne znam dobro šivati = I don’t sew well
• ali ovaj šav mogu popraviti = but I can fix this seam

So the overall meaning is: the speaker lacks the general skill, but can still handle this specific repair.

Not completely. Croatian word order is fairly flexible, but the given order is natural and neutral:

• Ne znam dobro šivati, ali ovaj šav mogu popraviti.

You may also hear variations like:

• Ne znam dobro šivati, ali mogu popraviti ovaj šav.

Both are understandable. The version with ovaj šav before mogu can put a little more focus on this seam.

Yes, in many contexts you may hear šiti as well. Both mean to sew.

However, šivati is a very common form and sounds perfectly natural here. For a learner, the important point is that both belong to the same verb idea, and usage can vary by style, region, or habit.

The direct object after popraviti is normally in the accusative.

So in this sentence:

• popraviti što? → ovaj šav

Because šav is masculine inanimate, the accusative looks the same as the nominative, which is why you see ovaj šav.