Cada vez que escribo deprisa, se me olvida el signo de interrogación o el de exclamación.

Cada vez que means every time (that). It highlights repetition very clearly.

• Cada vez que escribo deprisa... = Every time I write quickly...
• Cuando escribo deprisa... can also work, but it is a bit less explicit. Depending on context, cuando can mean when or whenever.

So here cada vez que is a very natural choice because the speaker is talking about a repeated habit.

Because the sentence describes a habitual action or something that generally happens.

Spanish often uses the present tense for this:

• Cada vez que escribo deprisa... = Whenever / every time I write quickly...

It is not talking about one specific moment, but about a recurring situation.

Yes. All three can express the idea of writing quickly, but they are not exactly identical in feel.

• deprisa = quickly, in a hurry
• rápidamente = quickly, more formally an adverb
• rápido is also often used adverbially in everyday speech: escribo rápido

In this sentence, deprisa sounds very natural. It often suggests not just speed, but a bit of haste.

Also, it is written as one word: deprisa.

Because Spanish very often expresses forgetting as something that happens to you, rather than something you actively do.

• Olvido el signo = I forget the mark
• Se me olvida el signo = literally something like the mark slips my mind

The second version is extremely common and very natural in Spanish, especially for everyday, unintentional forgetting.

So se me olvida often sounds more idiomatic than olvido in this kind of sentence.

In this structure:

• me = to me / for me
• se is part of the common pronominal pattern used with verbs like olvidarse

A useful way to understand it is:

• Se me olvida el signo
  = The mark gets forgotten by me / slips my mind

The important thing for learners is this:

• the thing forgotten is the grammatical subject
• the person who forgets is shown with me, te, le, etc.

So:

• Se me olvida el signo = I forget the mark
• Se te olvida el signo = You forget the mark

Because in Spanish clitic pronouns follow a fixed order. With a conjugated verb, these pronouns go before the verb, and se comes before me, te, le, etc. in combinations like this.

So you say:

• se me olvida
• se te olvida
• se le olvida

Not:

• me se olvida
• te se olvida

This is just one of those word-order rules you need to get used to.

Because the verb agrees with the grammatical subject, and here the subject is singular:

• el signo de interrogación o el de exclamación

That means the question mark or the exclamation mark — one or the other — so singular olvida is right.

Compare:

• Se me olvida el signo de interrogación.
• Se me olvidan los signos de interrogación.

Singular subject → olvida
Plural subject → olvidan

Because Spanish often avoids repeating a noun when it is already understood.

So:

• el signo de interrogación o el de exclamación

really means:

• el signo de interrogación o el signo de exclamación

The second signo is omitted because it would be repetitive. This is very common in Spanish.

A similar pattern is:

• Prefiero el rojo al azul
  = I prefer the red one to the blue one

Good question. Spanish does use both opening and closing signs:

• ¿ ?
• ¡ !

But the singular signo de interrogación or signo de exclamación can still be used to name that punctuation mark as a type, or to refer generally to the relevant mark that gets forgotten.

If you want to make it explicit that you mean both symbols together, you can use the plural:

• los signos de interrogación
• los signos de exclamación

So the singular here is normal and idiomatic.

Yes, people will understand both.

But in more standard or formal language:

• signo de interrogación is the usual formal term
• signo de exclamación is also very standard

You may also hear:

• signo de pregunta
• signo de admiración

Those are common alternatives, especially in everyday speech or when talking to children. In this sentence, interrogación and exclamación sound neutral and standard.

Because the sentence begins with a subordinate clause:

• Cada vez que escribo deprisa, ...

In Spanish, when this kind of introductory clause comes first, a comma is very common and standard.

So the structure is:

• introductory clause: Cada vez que escribo deprisa
• main clause: se me olvida el signo de interrogación o el de exclamación

The comma helps separate those two parts clearly.