This is the 3343rd most frequent Turkish word.
kafası
"Kafası" means "his/her/its head" in Turkish.
In this sentence, 'kafası' refers metaphorically to Ali's state of mind or focus.
Ali'nin kafası bugün hiç yerinde değil.
Ali seems very distracted today.
'Kafasını' here is used to signify the subject's thought process or mental capability being challenged.
Bu karışık problem kafasını karıştırdı.
This complicated problem confused him.
Here, 'kafasını' literally denotes the head's physical appearance.