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Eventhandler for TwinColSelect component
The client-side doesn't send those events, so you would have to modify the client-side logic in order to receive such events. You might be able to do this by either extending the client-side code (not sure, because there might be private methods/variables that you would need access to) or you might be able to do it using an extension.
The TwinColSelect is actually a fairly simple component that can be replicated completely on the server-side. An option is to replicate the functionality using a CustomField and a couple of ListSelects and then attach listeners to the them. I've actually created an add-on using this approach that adds functionality to the TwinColSelect. You can consider using that as a base for your implementation or extending/modifying my solution.