for adding 씨 to people’s names , is there a space or no space ?

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@rIchyhtlaeh2018lvyou 씨 can be used for 의존명사bound noun or 접사suffix. When '씨' comes after names or family names, it is 의존 명사 ‘씨’. You need a space here.
김 씨, 길동 씨, 홍길동 씨

But
'대한민국에는 김씨가 가장 많다'
For here, 씨 is suffix. It shows the family of 김, the family itself. In this case you don’t need a space.

​장 씨 아저씨가 그랬어.
장씨 성을 가진 사람들은 원래 착하다고.