[hjek]

How about just paraphrasing or echoing what they said? Like:

"I understand that you have difficulties figuring out how to acknowledge what others tell you without necessarily agreeing with what they said. In particular you find that nodding is problematic because of its ambiguity, and you are therefore interested in hearing how other people would deal with this issue."

Have you ever read any Marshall Rosenberg? He's all about that.

[zabaki]

I understand your point. But my "nod" is something that might be common for Scandinavians, as it is something we do while the other part is communicating.

So, as they make their point through a sentence, I nod/concur with the statement they made to show I understand and do not have a question regarding the statement (sometimes I would need clarification to fully grasp their point). After they are done I respond with either counter-argument or continue the conversation.