Where can I find the air pressure/weight guide for DT Swiss shocks? Or do all shocks have similar guidelines as far as pressure and rider weight goes?
The usual way to do this is to use the sag as a guide. The geometry of your frame will affect the load on the shock and the pressure you need.
To do this, put a zip-tie around the shaft of your shock*, or use the little rubber band if it has one and push it down against the seal. Next get dressed for riding and gently sit on your bike.
When you get off you'll be able to measure how for the shock moved under your weight. This is your sag.
Most people recommend between 10 and 20 percent of the total travel for sag.
* Not too tight, you don't want to damage the seal.