Ich bekomme den Fleck nicht weg.

Because Fleck is the direct object of the sentence, so it takes the accusative case.

• der Fleck = nominative, used for the subject
• den Fleck = accusative, used for the thing being affected

In Ich bekomme den Fleck nicht weg, I am the subject, and the stain is the thing I’m trying to remove, so German uses den Fleck.

It does usually mean to get or to receive, but in this expression it combines with weg to mean something like:

• to get rid of
• to remove
• to get off/out

So den Fleck wegbekommen means to get the stain off / out / removed.

This is a very common feature of German: a familiar verb can take on a more specific meaning when combined with a particle like weg.

Yes. wegbekommen is a separable verb.

Its full dictionary form is wegbekommen, but in a normal main clause it splits:

• Ich bekomme den Fleck nicht weg.

Here:

• bekomme = the conjugated verb in second position
• weg = the separated prefix, which goes to the end

Compare:

• Ich will den Fleck wegbekommen.
  With a modal verb, the full infinitive wegbekommen stays together at the end.

Because weg- is the separable prefix of wegbekommen.

In a standard German main clause, the conjugated part goes near the beginning, and the separable prefix moves to the end:

• wegbekommen → bekomme ... weg

So:

• Ich bekomme den Fleck nicht weg.

This is completely normal German word order for separable verbs.

Because the speaker is negating the result: they are saying they are not managing to get it away.

In this sentence, nicht wegbekommen works as a unit meaning not be able to remove / not succeed in getting rid of.

So:

• Ich bekomme den Fleck nicht weg. = I can’t get the stain out/off.

Putting nicht before weg is the natural placement here.

It absolutely can.

Both are possible:

• Ich bekomme den Fleck nicht weg.
• Ich kann den Fleck nicht wegbekommen.

The version with bekommen ... nicht weg is very idiomatic and common in everyday German. It often sounds a bit more natural in casual speech.

A rough difference:

• Ich bekomme den Fleck nicht weg. = I’m not getting the stain off / I can’t get it off.
• Ich kann den Fleck nicht wegbekommen. = I am unable to remove the stain.

The first often feels more practical and conversational.

It is neutral to informal everyday German and very natural in spoken language.

You could say it in many normal situations:

• while cleaning clothes
• while wiping a table
• while trying to remove a mark from a wall

In more formal or technical language, you might choose verbs like:

• entfernen = to remove
• beseitigen = to eliminate/remove

But for everyday speech, den Fleck nicht wegbekommen is very common.

Weg literally means something like away or gone.

In this sentence, it gives the idea that the stain should go away or be removed.

So the logic is roughly:

• den Fleck wegbekommen = to get the stain away

English often uses particles in a similar way:

• get off
• get out
• wipe away

German does this a lot with particles like weg-, ab-, aus-, auf-, and so on.

Yes. The exact English translation depends on the situation.

For example:

• from a table or wall: I can’t get the stain off.
• from clothing or fabric: I can’t get the stain out.

German den Fleck nicht wegbekommen is broad enough to cover both ideas. The context tells you what kind of removal is meant.

Yes. That is very common in spoken German.

• Ich bekomme den Fleck nicht weg.
• Ich kriege den Fleck nicht weg.

Both mean the same thing here.

The difference is mainly style:

• bekommen = a bit more neutral
• kriegen = more colloquial

In very casual speech, kriegen is extremely common.

A few very useful ones are:

• Ich bekomme das Etikett nicht ab.
  I can’t get the label off.

• Ich bekomme die Tür nicht auf.
  I can’t get the door open.

• Ich bekomme das Fenster nicht zu.
  I can’t get the window shut.

• Ich bekomme den Deckel nicht auf.
  I can’t get the lid open.

This pattern is very common in German:

• Ich bekomme + object + particle

It often means I can’t manage to make something open/closed/off/away.