Learn Farsi: واسه دونستن این راز خیلی کنجکاوم.

واسه is the everyday spoken replacement for the formal preposition برای (for). It acts exactly the same way and is extremely common in colloquial Tehrani Farsi.

Why is the word for "knowing" written as دونستن instead of its dictionary form دانستن?

In spoken Farsi, the "ā" sound frequently changes to an "u" sound when it comes directly before the letters "n" or "m". Because of this rule, the standard دانستن becomes the colloquial دونستن.

The English translation says "curious to know". Why does Farsi use واسه (for) plus the infinitive دونستن?

In Farsi, infinitives double as verbal nouns, acting like English words ending in "-ing". Because واسه is a preposition, it requires a noun object. So the sentence literally translates to "I am very curious for knowing this secret."

Could I phrase this sentence using a conjugated verb instead of the infinitive?

Yes! At the B1 level, you will often see this expressed with که (that) followed by the subjunctive mood: خیلی کنجکاوم که این راز رو بدونم (literally: I am very curious that I know this secret). Using واسه plus the infinitive is just a shorter, equally natural alternative.