가시나 has several meanings depending on the context.
There are 3 common usages.
1) noun. it means "little girl". it is a dialect of 계집애"little girl"
Not much disrespectful but very informal word used for addressing between intimate female friends or mother to daughter.
2) verb. it means "thorn grows". it is contracted form of 가시가 나. 가시(thorn) + 가(subject particle) + 나(grow)"
잎에 가시 나 The thorns grow on the leaf
3) verb. it means "Does she/he go". 가(go) + 시(honorific particle) + 나(interrogative ending suffix)
선생님은 언제 집에 가시나? When the teacher goes home?