50 minutes is KLM's minimum connection time for intercontinental connections at Amsterdam. The fact that they're willing to sell you the ticket indicates that they think it is at least common for passengers to be able to make it. After all, if you don't make it, they will have to pay to rebook you on another flight and pay EU compensation.
That being said, flying close to the minimum connection means that there is a realistic risk that you don't make it and have to be rebooked -- in particular if your incoming flight is even slightly delayed.
You may wish to call KLM and enquire whether it is possible to change your booking to one with a longer connection. They may or may not agree to that without charging exorbitant change fees.
Tell the cabin crew on the flight from Venice that you have a short connection and ask if they can offer any help with making the connection.
There's no interview you need to pass through in Amsterdam, and you will almost certainly get a boarding card for the transatlantic leg when you check in in Venice.
You need to pass through outbound passport control in Amsterdam, but that is quite painless when you're traveling with an EU passport. Some queueing can occur, though.
There's also generally an additional security check at the gate when departing on a flight to the US. But it's not likely to hold you up a lot; by the time you come running to the gate everyone else will already have been processed. And if you do hit a line there, they're not going to close the doors and depart while they're still processing passengers for that flight specifically.