This is the 17400th most frequent Turkish word.
üyesini
"Üyesini" means "its member" or "the member of it."
Here, 'üyesini' refers to a specific member of a club in the accusative case and is used as the direct object of the verb 'gördüm' (saw).
Kulüp üyesini toplantıda gördüm.
I saw the club member at the meeting.
In this sentence, 'üyesini' is in the accusative case, referring to a specific member being inquired after.
Bir derneğin üyesini sordular.
They asked about a member of an association.
The word 'üyesini' is used in the accusative case to refer to the direct object 'member of the book club' of the verb 'tanıyor musun?' (do you know?).