Learn Farsi: خواندن این دیوان خیلی سخت است. - Reading this poetry collection is very difficult.

In Farsi, when you use an infinitive as a noun (a gerund) followed by the thing being acted upon, they must be connected by an ezafe. You are literally saying 'the reading of this poetry collection' (khandan-e in divan).

If I wanted to use this lesson's formal grammar to say 'Reading one's own poetry collection is very difficult', how would I change the sentence?

You would drop این (this) and add the formal reflexive خویش (khish) or خویشتن (khishtan) after the noun. It becomes خواندن دیوان خویش خیلی سخت است (khandan-e divan-e khish kheyli sakht ast). Remember to add an ezafe to دیوان to link it to the pronoun!

Can I use divan for any type of book collection?

No, دیوان (divan) specifically means a collected volume of short poems by a single classical poet, like the famous دیوان حافظ (Divan-e Hafez). For a regular book series or collection, you'd use a word like مجموعه (majmu'e).

Why isn't the verb khandan at the end of the sentence?

Because in this sentence, خواندن (reading) is acting as the subject (a gerund noun), not the main action. The main verb is است (is), which correctly sits at the very end of the sentence.