These are certainly not the only shooting locations, but they are the most available. (Click on image to enlarge)
From position one, you will be able to catch players skating into the offensive zone, shooting, and checking. One thing you will probably not see is the face of the goaltender. The glass here is usually pretty dirty and more difficult to shoot through so, make sure you find a clean section to shoot through.
Position two will give you a great vantage point for photographing the goaltender. You sacrifice, however, players skating into the zone. From here, you’ll also be able to get close ups of players while facing off. This glass is a lot cleaner because the pucks rarely hit this section.
Another option (not in the diagram) would be to shoot from the stands, above the glass entirely. This will provide the sharpest images since the light does not have to pass through additional glass. The only problem is that the players will seem smaller in the photos compared to those shot from rinkside.
Personally I do not recommend using the holes. I have seen pucks, sticks, and other objects fly through the hole, which could easily damage equipment. There is always a place where you can shoot through the glass and get great pictures.