To view the support information, you need to wear the goggles and be holding a pickaxe (or sneaking). This will show you an overlay that indicates which blocks are supporting the target block (if any) with colors transitioning from green to red as the distance increases towards the limit. If there is only one support block, the color is slightly increased towards red as well, indicating the more precarious nature. The support rules used will be based on only the information that can be known by the player from looking. This means that Fractured Stone that is completely surrouneded on all four sides will be treated as smooth unstable stone, even though it is not a valid support. The same goes for blocks in the corner between a wall and ceiling, such as dirt.
When looking at the top side of a block, it will simply display as green (is supported) or red (not supported).