Assuming you're referring to the MIDIPiano example project - that uses an iterator together with Iterator notes from a single MIDI source.

- The Source is where you configure the MIDI source.
- Screenshot 2023-01-12 213129.png (17.78 KiB) Viewed 695 times
If you want to have two physical keyboards control one virtual keyboard then add a second node for each node that uses iterator notes. Configure these duplicates to use your second midi source. If you hit the same key on both keyboards simultaneously you'll get double the effect.
If you want to have each physical keyboard control different parts of the virtual keyboard then you'd have to split the virtual keyboard with two separate iterators. I'm not sure how you could limit the iterator notes though.