Let er ook op dat je naam bovenaan het formulier staat.

It comes from the separable verb opletten, which means to pay attention or to make sure.

• opletten = to pay attention
• op iets letten = to pay attention to something

In this sentence, Let ... op dat ... means something like:

• Make sure that ...
• Pay attention that ...

So Let er ook op dat je naam bovenaan het formulier staat means Also make sure that your name is at the top of the form.

This is a very common Dutch structure.

Dutch often uses er + preposition when referring to something in a general way, especially before a clause like dat ....

Here:

• op letten = to pay attention to
• er ... op letten dat ... = to make sure that ...

So er does not mean there here. It is part of the fixed pattern erop letten dat ....

You can think of it as a grammatical placeholder:

• Let erop dat ...
• Let er ook op dat ...

Because ook is inserted, erop gets split into er ... op.

Both ideas are related, but Dutch often splits erop when another word comes in between.

Compare:

• Let erop dat je naam bovenaan het formulier staat.
• Let er ook op dat je naam bovenaan het formulier staat.
• Ik reken erop.
• Ik reken er niet op.

So erop can appear:

• as one word when it stays together
• split as er ... op when something like ook, niet, or another word is placed between them

That is why Let er ook op is perfectly normal.

ook means also or too.

It shows that this is an additional instruction:

• Also make sure that your name is at the top of the form.

Its position is natural in Dutch:

• Let er ook op dat ...

Placing ook there gives emphasis to the idea that this is one more thing to remember.

Both are possible, but they are used differently.

• je = unstressed your
• jouw = stressed your, often used for emphasis or contrast

So:

• je naam = your name
• jouw naam = your name, with extra emphasis

In a neutral instruction, Dutch usually uses je:

• Let erop dat je naam bovenaan het formulier staat.

If you wanted contrast, you might use jouw:

• Niet zijn naam, maar jouw naam.

Because after dat, Dutch uses subordinate clause word order.

In a dat-clause, the finite verb usually goes to the end:

• main clause: Je naam staat bovenaan het formulier.
• subordinate clause: ... dat je naam bovenaan het formulier staat.

So the order is:

• dat
  • subject + other information + verb

This is one of the most important Dutch word order patterns to learn.

Dutch often uses staan for text or objects that are positioned somewhere, especially on paper, signs, screens, lists, and forms.

So:

• Je naam staat bovenaan het formulier. = Your name is written/shown at the top of the form.

This is more natural in Dutch than is.

Compare:

• Mijn adres staat op de brief.
• De datum staat linksboven.
• Wat staat er op het bord?

English often uses is, but Dutch frequently uses staan in these cases.

bovenaan means at the top.

It is built from:

• boven = above / up
• aan = on / at

Together, bovenaan means something like at the top position.

Examples:

• Mijn naam staat bovenaan de lijst.
• Zet de titel bovenaan de pagina.

So bovenaan het formulier means at the top of the form.

Because formulier is a het-word in Dutch.

So:

• het formulier = the form
• een formulier = a form

Unfortunately, grammatical gender in Dutch often just has to be learned word by word. There is not always a reliable rule you can guess from.

It is fairly neutral, but je naam makes it sound informal or semi-neutral.

• je = informal your
• uw = formal your

A more formal version would be:

• Let er ook op dat uw naam bovenaan het formulier staat.

So the original sentence is the kind of thing you might see in instructions aimed at the general public, students, or users in a friendly tone.

Yes. Let is the imperative form of letten.

So the sentence begins with a command or instruction:

• Let op! = Pay attention!
• Let er ook op dat ... = Also make sure that ...

Dutch often uses the imperative in instructions, notices, and directions.

Yes, there are several natural alternatives, for example:

• Zorg ervoor dat je naam bovenaan het formulier staat. = Make sure that your name is at the top of the form.

• Controleer of je naam bovenaan het formulier staat. = Check whether your name is at the top of the form.

• Let erop dat je naam bovenaan het formulier staat. = Make sure that your name is at the top of the form.

These are similar, but the original sentence sounds like a straightforward instruction telling someone to pay attention to this detail.