One of my favorite features in Android Wear was removed with the release of 2.0. Before AW 2.0 when you would activate DND on your watch it would also toggle on DND on your phone. After AW 2.0 you have to enable DND separately on both devices.
The best solution I've found to this problem so far is an app called Do Not Disturb Sync for Wear. This app doesn't toggle DND on your phone but it will do the next best thing and silence your phone. It's not ideal if you rely on priority contacts feature of DND, but it's great if you just want to silent both devices at once. Whether it's because you're in a meeting, going to a movie, or just want a break this app is fantastic.
First you'll want to download the app to your phone, open it, and you'll be prompted give it access to your notifications. Next you'll want to install it on your watch. Open the Play Store and scroll to the bottom, it should show up in the list of apps that are on your phone that can be installed on your watch. Once it is installed on your watch open it and then you should be ready. Now when you toggle DND on your watch it will silence your phone and toggling it off will turn off silent on your phone.