To view all future scheduled custom messages in one place go to your messages tab and click on the message type you are looking for. 

Step 1: Go to "Messages" page.

Step 2: Choose the type of message you want to view.

Step 3: Done!

You can also see all future scheduled custom message for a specific client.

Step 1: Go to the customer record > upcoming messages .

Step 2: Click on "Custom Messages" to view.

Step 3: Done!