what was written on the back of hotel research?

We don't see it, that's the point.
We need to use our imagination.

I'm going to say it's an invitation to meet him again. Or a phone number?

Or just some random graffiti like the back of the pictures hanging in the hotel rooms

They focus on the question they left unanswered on the feedback sheet asking if they would come again. She then glances down to where he's written turn over. I think he simply wrote yes. In reference to her. Maybe with his number. Maybe not. I'm normally someone who needs answers and doesnt like open ended movies, but i actually really appreciated and enjoyed it here.