Learn Turkish: Gelen ziyaretçiler caminin nerede olduğunu broşürden okuyabilir. - The incoming visitors can read where the mosque is from the brochure.

To form an indirect question, Turkish uses the question word (nerede) followed by the factive clause form of the verb. Since the verb is "to be" (where it is), we use olmak (to be) and add the -dık suffix. With the possessive suffix, this becomes olduğu. Literally, the phrase means "the mosque's where-being."

Why does cami (mosque) have the genitive suffix -nin attached to it?

In Turkish factive clauses (clauses ending in -dık or -acak), the subject of that sub-clause must take the genitive case. Since "the mosque" is the subject of the clause "where the mosque is", cami becomes caminin. It pairs directly with the possessive suffix on olduğu.

Why is there an extra -nu at the end of olduğunu?

The whole phrase caminin nerede olduğunu is the direct object of the main verb, okuyabilir (they can read). Because it is a specific direct object, it requires the accusative case suffix -u. The -n- in the middle is a buffer letter separating the possessive and accusative suffixes.

What is the grammar behind the word gelen?