Learn Hardcore Hungarian: A diák sokat tanul.

A is the Hungarian definite article, equivalent to English the. It marks that we’re talking about a specific student. Without it you’d use Egy diák (a student) for the indefinite meaning, or omit the article only in certain special contexts.

Why is the word sokat used instead of sok?

sok is an adjective meaning many/much when placed before a noun (e.g. sok könyv = many books). To modify a verb, you need the adverbial form sokat (with the -at suffix), which means a lot (in terms of how much someone does something). Hence sokat tanul = studies a lot.

What part of speech is sokat, and what question does it answer?

sokat is an adverb of quantity. It answers the question Mennyit? (How much?).
Example:
– Mennyit tanul a diák?
– Sokat. (A lot.)

Why doesn’t tanul carry a suffix for 3rd person singular? How do we know who is doing the studying?

In Hungarian, the 3rd person singular indefinite verb form carries no ending (root form). Here tanul is indefinite because there’s no definite direct object. The subject A diák is explicitly stated, so we know it’s 3rd person singular. Hungarian often drops personal pronouns, but with nouns like A diák, you simply state the noun and use the root-form verb.

How would you change the sentence to talk about multiple students studying a lot?

– Make diák plural: diák → diákok (plural suffix -ok matches the back vowel á).
– Use the 3rd person plural indefinite verb ending -nak: tanul → tanulnak.
– You can keep or drop the definite article for general statements.
So:
A diákok sokat tanulnak. (The students study a lot.)
Or for a generic statement:
Diákok sokat tanulnak. (Students study a lot.)

Is the word order fixed as A diák sokat tanul, or can we rearrange these elements?

Hungarian word order is flexible and driven by topic–focus. In A diák sokat tanul, A diák is the topic and sokat tanul is the comment. If you say Sokat tanul a diák, you put emphasis on sokat (it’s really a lot). The neutral SVO order is what you see in the original.

How do you turn A diák sokat tanul into a question (“Does the student study a lot?”)?

Spoken style usually just uses rising intonation without changing word order:
A diák sokat tanul?
In a more formal or written style you can add the interrogative particle -e to the verb and rearrange:
Tanul-e sokat a diák?

If you want to express that the student is studying right now a lot, how do you show that ongoing action?

Hungarian doesn’t have a separate progressive tense. You convey “right now” with adverbs like éppen (just) or folyamatosan (continuously):
A diák éppen sokat tanul.
A diák folyamatosan sokat tanul.
The verb stays the same.