I want to show that status on openhab
The lamp is configure with KNX device and I use the switch function on openhab. But with the switch I don’t have the because I have 1 group adress for the switch and on another group adress for the state
Why? This is conceptual misunderstanding. Just use the status of the existing switch type item and you should be fine.
You can also configure a switch type item to more than one channel (= KNX GA) so you can specify to send commands to GA 1 but receive (and propagate into OH) the state from GA 2.
You can even configure another (second !) ‘switch’ type item for the ‘state’ address as, which by default will display as ON/OFF, but again you have a misconception here.