Learn Turkish: Vatandaşlık alacağı zaman bu evrakları hazırlayacak. - When he is going to get citizenship, he will prepare these documents.

It uses the future participle -acak combined with a possessive suffix. The root is al- (to get/take). We add -acak for the future meaning, and then the 3rd person singular possessive -ı (his), making it literally "at the time of his future getting".

Why does the future suffix -acak change to -acağ- in alacağı?

This is a standard consonant mutation. When the possessive suffix -ı (a vowel) is added to -acak, the final k softens to a ğ. You will see this happen almost every time you use this future "when" structure with subjects other than "they".

Why does evrakları have the -ı suffix at the end?

The suffix -ı is the specific accusative case marker. Because the sentence says he will prepare bu evrakları (these specific documents), they are the specific direct object of the verb hazırlayacak, which requires the accusative ending.

Since evrak originally means plural "documents", why do we add the plural suffix -lar to it?