素敵な景色‼️ 本当にすごいでしょうね? ( wonderful scenery. It's really great isn'it? ) Does this sound natural?

I wouldn't understand exactly what you mean without the English translation provided.

1. It should be either すごいでしょう (It's great, isn't it?) or すごいですね (I agree that it's great.)

2. It will sounds a little bit strange if both sentences are said by the same person. If person A said 素敵な景色 then the person A should have said 本当にすごいです or 本当にすごいですね in the sense of "You were right when you told me that this scenery would be great." It should be person B who says 本当にすごいですね to agree with the statement of person A 素敵な景色！ or 本当にすごいでしょう confirming his own statement previously told to the person A that this scenery would be great.