Learn Hardcore Dutch: De professor geeft duidelijke feedback op elke paragraaf. - The professor gives clear feedback on every paragraph.

Dutch nouns are either de-words (common gender) or het-words (neuter).
Professor is a common-gender noun, so it always takes de: de professor.
You would only use het with neuter nouns, like het boek (the book), het kind (the child).
So: de professor, een professor, de goede professor are all correct.

What form of the verb is geeft, and why is it in second position?

Geeft is the third-person singular present form of geven (to give):

ik geef
jij/u geeft
hij/zij/het geeft

In a normal main clause, Dutch has verb-second (V2) word order: the finite verb must be in the second position.
Here, the first “slot” is taken by the subject De professor, so the verb geeft must come right after it.

Why do we say duidelijke feedback and not duidelijk feedback?

In Dutch, adjectives before a noun usually get an -e ending.
Feedback is a de-word (de feedback), so any adjective in front of it gets -e: duidelijke feedback, goede feedback, constructieve feedback.
The only common case where you don’t add -e is with singular, indefinite, neuter (het-) nouns, e.g. een duidelijk boek, een mooi kind.
Since feedback is not neuter, you must say duidelijke feedback.

Is feedback countable in Dutch, and does it change in the plural?

In Dutch, feedback is usually treated as an uncountable noun, like in English.
You normally say de feedback, een beetje feedback, veel feedback, not twee feedbacks.
You may see feedbacks in some informal or business contexts, but it still sounds foreign or jargon-like.
So you keep it as feedback and show quantity with other words (veel, weinig, extra, goede, etc.).

Why do we use the preposition op in feedback op elke paragraaf?

With the noun feedback, Dutch commonly uses the pattern feedback op X (“feedback on X”):

feedback op de tekst – feedback on the text
feedback op je werk – feedback on your work
feedback op elke paragraaf – feedback on each paragraph

You can sometimes see feedback over in more general contexts, e.g. feedback over de cursus (feedback about the course).
But when you mean detailed comments tied to specific parts (paragraphs, sentences, slides), feedback op is the most idiomatic.

What is the difference between elke and ieder(e) here? Could I say op iedere paragraaf?

Both elke and ieder(e) can mean “each / every”, and both are correct here:

op elke paragraaf
op iedere paragraaf

In many contexts they are interchangeable.
Elke is slightly more common and a bit more neutral or everyday.
Ieder(e) can sound a touch more formal or emphatic in some contexts, but the difference is small.

Why is it elke paragraaf and not elke paragraafS like English “every paragraphs”?

In Dutch, as in English, elke / iedere / elkeen / ieder is followed by a singular noun:

elke paragraaf – every paragraph
elke student – every student
iedere week – every week

To talk about all paragraphs in general, you would use the plural with alle:

alle paragrafen – all paragraphs.
So: elke paragraaf (singular), alle paragrafen (plural).

What gender is paragraaf, and what is its plural?

Paragraaf is a de-word: de paragraaf.
Its plural is paragrafen:

de paragrafen – the paragraphs
op alle paragrafen – on all paragraphs

So you say: de paragraaf, de paragrafen, elke paragraaf, alle paragrafen.

Can I change the word order to De professor geeft op elke paragraaf duidelijke feedback?

Yes, that word order is also correct.
Both of these are fine:

De professor geeft duidelijke feedback op elke paragraaf.
De professor geeft op elke paragraaf duidelijke feedback.

Dutch allows some flexibility in the order of objects and prepositional phrases.
Changing the order can shift the emphasis slightly (e.g. putting op elke paragraaf earlier can highlight “on each paragraph” more), but grammatically both sentences are acceptable.

How would I say this sentence in the past or future in Dutch?

Base sentence (present):

De professor geeft duidelijke feedback op elke paragraaf. – gives

Simple past (imperfect):

De professor gaf duidelijke feedback op elke paragraaf. – gave (habitually or in a specific past context)

Present perfect:

De professor heeft duidelijke feedback gegeven op elke paragraaf. – has given / gave

Future with “zullen”:

De professor zal duidelijke feedback geven op elke paragraaf. – will give