How to see blocked messages

If you have blocked someone, you won't see SMS or iMessages from them. That's the point of blocking them.

If you simply don't want to be notified when a particular person messages you, you can hide alerts from that person. On the main conversation screen in Messages, find the conversation from that person. Place your finger on the listing and slide to the left. Tap "Hide Alerts". The messages will still show on your phone but you won't be notified of their arrival.