Not sure I understand the question. The event notifications (and this is true to most Kaltura objects) are per partner ID. On different ENVs (and even on the same one when you have multiple partners), you will have several different partner IDs and so, you can set the endpoint to which to send the info per notification (you can also configure several different types of notifications per partner).
Please reiterate your question if the above does not answer it.
In your original post, you’ve mentioned 3 different ENVs. Naturally, these do not share the same DB or else, they would not be different ENVs.
If that’s not the case, please explain exactly what your use case is and what you’re trying to accomplish and I’ll provide further guidance.
The relationship between partners and users is explained in this post Kaltura Media Center kmc1 file