Can I make a Reflection Unit token of a Reflection Unit token?

Yes, you can create a Reflection unit token that is a copy of another Reflection unit token.

According to Rule 182.1.d, token units are units and follow all rules for their type. When a Reflection token enters play, it becomes a copy of a target unit already in play. If you target an existing Reflection token, the new Reflection token will copy the current characteristics of that token (including the card it is currently copying, as those are its current traits).

This is consistent with how copying works in Riftbound: when an object becomes a copy of another, it adopts the current characteristics of the target. Since a Reflection token is a unit, it is a valid target for another Reflection effect.