Are you asking about how much air pressure the wheel can take? Or are you asking what the load rating of the wheel is (how much weight it can carry) Rest assured the wheel can take more air pressure than you should EVER subject your tires to, so no worries there (unless the wheel has a crack or a flaw in it already) For tire pressures either follow what is written on your tires or what is on the label on the door jam.
If you're asking about the load rating of the wheel, pull one off & look on the inside wheel surface. It may/should be cast in to the surface. Mine are 2950 lbs each & the numbers were cast in when they were built. You may be able to use a flashlight & see it through the spokes without taking the wheel off.