Wenn ich die Fehlermeldung auf dem Bildschirm sehe, überprüfe ich das Dokument noch einmal.

Because Wenn ich die Fehlermeldung auf dem Bildschirm sehe is a subordinate clause introduced by wenn.

In German, when a clause starts with a subordinating conjunction like wenn, the conjugated verb goes to the end of that clause.

So:

• wenn = subordinating conjunction
• ich = subject
• die Fehlermeldung = object
• auf dem Bildschirm = prepositional phrase
• sehe = verb, placed at the end

This is a very common German pattern:

• Wenn ich Zeit habe, ...
• Weil er müde ist, ...
• Dass sie kommt, ...

So the verb-final position after wenn is completely normal.

Because the sentence begins with the wenn-clause, and in German that entire clause counts as position 1 in the sentence.

German main clauses usually follow the verb-second rule: the conjugated verb must come in position 2.

So the structure is:

1. Wenn ich die Fehlermeldung auf dem Bildschirm sehe
2. überprüfe
3. ich
4. the rest of the sentence

That is why you get:

• Wenn ..., überprüfe ich ...

and not:

• Wenn ..., ich überprüfe ... ❌

This is one of the most important German word order rules.

Here, wenn means when in the sense of whenever or if/when this happens.

In this sentence, it suggests a repeated or general situation:

• Wenn ich die Fehlermeldung auf dem Bildschirm sehe, überprüfe ich das Dokument noch einmal.
• Whenever I see the error message on the screen, I check the document again.

Compare:

• wenn = when / whenever / if, for repeated events or conditions
• als = when, for a single event in the past
• wann = when? in a question or indirect question

Examples:

• Wenn ich Hunger habe, esse ich. = Whenever I’m hungry, I eat.
• Als ich jung war, ... = When I was young ...
• Wann kommst du? = When are you coming?

So wenn is the correct choice here.

These are the nouns’ grammatical genders:

• die Fehlermeldung = feminine
• das Dokument = neuter

You simply have to learn nouns together with their articles.

In this sentence, both nouns are also in the accusative case because they are direct objects:

• ich sehe die Fehlermeldung
• ich überprüfe das Dokument

For these two nouns, the accusative forms happen to look the same as the nominative:

• feminine: die stays die
• neuter: das stays das

So nothing changes visibly here, but they are still accusative objects.

Because auf is a two-way preposition. That means it can take either:

• dative for a location
• accusative for a direction/change of position

Here, auf dem Bildschirm describes where the error message appears: on the screen. That is a location, so German uses the dative:

• auf dem Bildschirm = on the screen

If it meant movement onto the screen, then accusative would be used:

• Ich lege das Symbol auf den Bildschirm. = I put the icon onto the screen.

So:

• Where? → dative → auf dem Bildschirm
• Where to? → accusative → auf den Bildschirm

Noch einmal means once again, one more time, or simply again.

In this sentence:

• überprüfe ich das Dokument noch einmal
• I check the document again / one more time

It suggests repeating the action, often for safety or confirmation.

German also has wieder, which can often mean again too. But there can be a slight difference:

• noch einmal = one more time, often emphasizing repetition
• wieder = again, often just stating that something happens again

In many everyday contexts, both are possible, but noch einmal can sound a bit more like once more.

No, überprüfen is not separable.

That is why you say:

• ich überprüfe
• ich habe überprüft

and not:

• ich prüfe ... über ❌

German has many verbs with prefixes, and some are separable while others are inseparable. über- can be either one depending on the verb, but in überprüfen it is inseparable.

Compare:

• überprüfen = to check, verify → inseparable
• überfahren can be separable or inseparable depending on meaning and stress

So in this sentence, überprüfe stays together as one verb form.

Because each clause needs its own subject.

The first clause has:

• ich ... sehe

The second clause has:

• ich ... überprüfe

Even though English sometimes feels a bit lighter in repeating subjects, German normally keeps the subject explicitly in each clause unless there is a special reason not to.

So this is standard and necessary:

• Wenn ich ..., überprüfe ich ...

Because in German, all nouns are capitalized.

So:

• die Fehlermeldung
• der Bildschirm
• das Dokument

This is one of the easiest visual clues in German: if a word is capitalized in the middle of a sentence, it is usually a noun.

Adjectives, verbs, and most other words are not capitalized unless they begin the sentence or are part of a special case.

A rough breakdown is:

• Wenn = when / whenever
• ich = I
• die Fehlermeldung = the error message
• auf dem Bildschirm = on the screen

• sehe = see

• überprüfe = check / review
• ich = I
• das Dokument = the document
• noch einmal = once again / again

So the structure is roughly:

When I the error message on the screen see, check I the document once again.

That sounds unnatural in English, but it helps show how German word order works.

Yes. That would still be correct.

• Wenn ich die Fehlermeldung sehe, überprüfe ich das Dokument noch einmal.

The phrase auf dem Bildschirm just adds extra information about where you see the error message.

So:

• with auf dem Bildschirm = more specific
• without it = still grammatical, just less detailed

Most naturally, it sounds like a general habit or repeated reaction:

• whenever I see that message, I check the document again

German often uses the present tense for this kind of meaning.

Depending on context, it could also refer to a future situation:

• When I see the error message, I’ll check the document again.

German does not always need a special future form to express future meaning. The present tense often does the job if the context makes it clear.

So this sentence can work for:

• a habit
• a routine response
• a future action in context

But without extra context, it most naturally sounds like a general repeated action.