What should I play against the Trompowsky?

I don't face it a lot, but what is a good response? 

the kamalapowsky

lol. its a real opening tho. it is 1.d4 Nf6 2.Bg5

Your problem is, that despite what you play, the resulting positions will be rather uncommon for you and common for White. That is why we like to play the Tromp :-)

So decide what suits you best between the main moves 2...Ne4, 2...d5, 2...c5 or 2...e6 - or decide to specialize in a more rare move, that may be not as good, but also unknown to your opponent.

Even 2...h6 is a perfectly good answer if you follow 3.Bxf6 exf6 with a good development plan.

I like 2... d5 to try and provoke 3. Nf3 so 3... Ne4 is possible.

2...d5 is fine, but it won't provoke 3.Nf3 unless you are facing a noob.

What you will see FAR more often after 2...d5 is either 3.Bxf6, 3.e3, or 3.Nd2

The hillaryowsky has also been used against this opening with very little success.

Seriously though, an interesting bit of trivia is that the Trompowsky was used by Carlsen in the first round of the 2016 world chess championship. He did it as a nod to the president elect.

I played the Tromp on and off for over 10 years when I was an active player. The move I liked facing the least was probably 2…e6 as I didn’t enjoy the positions as much and I never really studied them. Normally used by players who just wanted to get a game and play chess. 

When they played 2…Ne4 it normally meant Black had a bit of theory prepared as they have to be ready for Bf4, Bh4 and h4. This was probably the line I liked facing the most as it’s what I played as Black so I knew it fairly well.

2…d5 is a solid move and often the move played at top level when the opponent wheels out the Tromp but (as mentioned above) it would not provoke Nf3 against a decent player. 

2…c5 is a good move - the positions are a bit more non-standard so you need to have a basic idea of what you’re aiming for. 
There’s some other moves as well but I feel that most of the others give white more chances to get some sort of advantage and I was normally pretty happy to see any move not mentioned above. 

Thank you!

I play the Tromp myself, but not because of some orange spray-tan buffoon!

Who knows, maybe when you become the best player in the world and rack up a few world championship wins you might change your mind. Although like Carlsen, I have to admit it's nice to see things get back on track again.

I like 2...e6 followed by 3...h6, putting the question to the bishop.

I like Ne4 and c5