Welcome to the Community 🙂 Thanks for reaching out about this.
At the moment, the shuffle button in your Discover Weekly can be found in the three-dot menu in the Now Playing view, on the top of your screen. You can also find it as a green button that says "shuffle play" under the playlist's cover when you open it.
On the other hand, some users also think it would be a good idea to keep this in a visible place. In this case, we'd recommend to add your +Vote and Subscribe to this thread. That way you can stay up-to-date with any relevant news about this.
If you have any other questions, don't hesitate to let us know.