Backchanneling is the feedback that listeners give to show that they are listening.
This is often a culture-dependent question because often people make "listening noises" without even thinking about it. You will find this the case even with very fluent speakers. A few ideas to get you started:
- mi aŭdas
- kaj poste?
If you find your speaking partner reacting in unexpected ways to certain phrases, use another phrase. Even "mmm" and "uh huh" will work.