Clients support Yggdrasil for P2P connections out-of-the-box as long as both sides have Yggdrasil running on their computers. The server does not need to have Yggdrasil running, but if it does, it will be able to verify reachability of clients through Yggdrasil for extra assurance.

As long as you have IP probing enabled in your client settings (enabled by default), you do not need to do anything special to enable Yggdrasil support.