Learn Croatian: Jeste li pročitali ovu knjigu?

pročitali comes from pročitati, which is the perfective version of the verb "to read". We use perfective verbs when we care about the completion or result of an action. Here, we are asking if you finished reading the book. If we used the imperfective čitali, the question would mean "Were you reading this book?" which focuses on the activity itself rather than whether you finished it.

Why does the verb pročitali end in -i?

In the Croatian past tense, the main verb acts like an adjective and has to match the subject. The -i ending is for masculine plural. We use this plural form either because we are asking a group of people ("Have you all read..."), or because we are talking to one person using the polite, formal "you" (Vi).

Why is it ovu knjigu instead of ova knjiga?

The book is the direct object of the sentence because it is the thing being read. Therefore, it must be in the accusative case. For feminine nouns ending in -a like knjiga, the ending changes to -u to become knjigu. The word for "this" (ova) also has to match that grammatical case, becoming ovu.

Why does the sentence start with Jeste li instead of just using ste?