Where is trash in new Photos app?
There is no Trash any more - instead there is Recently Deleted, same as on the iPhone etc. which will countdown 30 days before final deletion unless purged manually or recovered beforehand.

In OS X 10.10 Yosemite, you can access it from the File Menu > Show Recently Deleted. In OS X 10.11 El Capitan, there is no menu item, but it can be accessed from the "Albums" tab, where you'll find the recently deleted folder in the familiar shape of the trash bin of yore.

You exit, once finished, by clicking any other category, or if you don't have the Sidebar open, any Header - Albums etc.