This is the 16059th most frequent Turkish word.
vagonun
"Of the wagon" or "of the carriage."
In this sentence, 'vagonun' is the genitive form of 'vagon' (wagon), indicating possession of the interior space of the wagon.
Vagonun içinde yolcular yerlerini aldı.
The passengers took their seats inside the wagon.
Here, 'vagonun' expresses a possessive relationship, linking the door to the wagon (the door belongs to the wagon).
Vagonun kapısı hala açıktı.
The door of the wagon was still open.
In this usage, 'vagonun' indicates possession, referring to the new model belonging to the wagon.