Do you need "a" in this expression?

Yes.
Bt it's much more common to say 'as a Japanese person'.

teacherJapan From my viewpoint as (a) Japanese, I was surprised when she said that.

Some people (including me) think that "a Japanese" is bad English. Other people may accept it.

I see! A Japanese person is a better choice:) Thank you very much, all:)

It just hit me. So if I were someone from America, should I say "From my viewpoint as an American person" Or should I say "From my viewpoint as an American?"

teacherJapan"From my viewpoint as an American?"

That's fine. It's the ese-adjectives and nouns that are different grammatically.

CB