This is the 5356th most frequent Turkish word.
kimliğinin
"Kimliğinin" means "of your identity" or "of his/her/its identity" depending on context.
In this sentence, 'kimliğinin' refers to 'your identity' in possessive form, denoting ownership of the concept of identity.
Kimliğinin doğruluğunu kanıtlaman gerekiyor.
You need to prove the validity of your identity.
Here, 'kimliğinin' indicates 'identity card' with possessive form, contextualizing the physical document as owned by the individual.
Kimliğinin kaybolmasından endişe ediyor.
He/She is worried about losing his/her identity card.
In this case, 'kimliğinin' stands for 'your identity' in terms of personal, social, or legal presentation, demonstrating its abstract definition in possessive form.