Learn Turkish: Patronun belgeyi imzalaması şaşırtıcı olacak mı? - Will it be surprising for the boss to sign the document?

This is how Turkish forms an action subject clause. Instead of saying "for the boss to sign," Turkish essentially says "the boss's signing." The person doing the action (patron) takes the genitive case (-un), and the short verbal noun (imzala-ma) takes the matching possessive suffix (-sı). The entire phrase Patronun belgeyi imzalaması acts as the subject of the sentence.

If imzalaması is acting like a noun, why does belge take the accusative suffix -yi?

Verbal nouns in Turkish have a split personality! Externally, the whole phrase acts like a noun phrase. But internally, the word imzalama still acts like a verb and can take a direct object. Because the boss is signing a specific document, the verb imzalamak still demands the accusative case on belgeyi.

How is the adjective şaşırtıcı (surprising) formed?

It is built in three steps. It starts with the root verb şaşmak (to be surprised). Adding the causative suffix turns it into şaşırtmak (to surprise someone). Finally, the suffix -ıcı turns the verb into an adjective that describes the thing causing the action, giving us şaşırtıcı (surprising).