Final answer:
The sentence "Su camisa es bonita" is grammatically correct and the subject is "Su camisa" which means "His/Her shirt".
Step-by-step explanation:
The given sentence "Su camisa es bonita" is grammatically CORRECT. In Spanish, the subject of a sentence is often indicated by the verb form. In this sentence, the verb "es" is conjugated in the third person singular form, indicating that the subject is singular. Therefore, the subject of the sentence is "Su camisa", which means "His/Her shirt".
Learn more about Spanish sentence structure