First of all make sure your lamp is configured properly in Thinka (see KNX) as a switch or lightbulb. The name should be easily pronounceable and unique, such as “floor light”. Then you can just say: “Alexa, turn on the floor light”.
In case something is not clear or not working according to your expectation you can contact us, and we will provide instant feedback. We can be reached by email at firstname.lastname@example.org, or by phone at +31-20-2420666