Learn Farsi: دو دهه است که در مورد ارتباط دیجیتال تحقیق می‌کنند. - They have been studying digital communication for two decades.

This is the core of the current lesson! When an action started in the past and is still happening right now, Farsi uses a time phrase plus است که (ast ke) followed by the Present Indicative. Literally, it translates to "It is two decades that they are researching." You don't use a past or perfect tense here like you do in English.

I don't see the word for "they" in the Farsi sentence. How do we know who is studying?

The subject pronoun آنها (aanhaa) is dropped, which is very common in conversational and written Farsi. We know the subject is "they" because of the -ند (-and) personal ending on the verb می‌کنند (mikonand).

What exactly does در مورد mean and how is it connected to the rest of the sentence?

در مورد (dar mored) is a very useful compound preposition that means "about", "concerning", or "regarding". To connect it to the topic they are researching (ارتباط دیجیتال), you must use the invisible ezafe vowel sound, making it pronounced dar mored-e.

Why is "digital communication" written as ارتباط دیجیتال instead of the other way around?

In Farsi, nouns almost always come before the adjectives that describe them. ارتباط (ertebaat) means "communication" and دیجیتال (dijitaal) means "digital". They are linked by the spoken ezafe, so you pronounce it ertebaat-e dijitaal.