Learn Farsi: کدام گل استوایی مثل نیلوفر معطر است؟ - Which tropical flower is fragrant like the lotus?

It is built from the noun ostova (the equator). By adding the relative suffix -i, it becomes an adjective meaning equatorial or tropical. The -y- in the middle is added to bridge the vowels because ostova ends in a long vowel, making it flow smoothly as ostovayi.

Is the word mo'attar (fragrant) related to the English word attar (as in rose attar)?

Exactly! Both come from the same Arabic root for perfume. In Farsi, the noun is atr (perfume or cologne), and mo'attar is the adjective form meaning perfumed, scented, or fragrant.

Why is the comparison mesl-e nilufar placed before the adjective mo'attar?

In Farsi word order, prepositional phrases showing comparison typically come right before the adjective they modify. While English says fragrant like a lotus, Farsi naturally says like a lotus fragrant.

Since this lesson teaches az jomle (including / among which), how could I use it to answer this question?

You can use az jomle to single out a specific flower from a larger group. For example, you could answer: Many tropical flowers are fragrant, including the orchid (Gol-haye ostovayi-ye ziyadi mo'attar hastand, az jomle orkideh).