I just gave a detailed answer on how to do this, on your other post:
Btw, can I make two humble and friendly suggestions?
First, a better post title may have been “Can Reaktor Send MIDI to a Synth in Cubase?”
Me, the person with the answer, almost didn’t click on your post (you lucked out).
If I had seen “Reaktor” in the title, I would have clicked on it for sure.
Second, two posts asking the same question within a few days of each other is redundant.
Better to post one, well-named post and “bump” it yourself (add a new reply to it), if you have to.
Cheers!