Cvettester.....Let's start at the front. Your steering column should have three fittings. One is visible from underneath, one is half way up the steering column shaft and can usually be accessed with the generator slid out. The third one is under the cover of your steering column, inside the coach.
The front end has it on both the top and bottom of the kingpins. All of the steering links and the brake assembly (cans/slack adjusters).
The drive shaft has two on each u-joint and as mentioned, you only need to get to one to fill the entire u-joint. The slip joint on the driveshaft has an obvious fitting, but you have to find the relief hole at the end of the slip joint, between the slip joint and u-joint. Usually, you can reach your middle finger in there and cover the relief opening while you pump grease into the slip joint until it oozes out of the end of the slip joint (spline end).
The rear end has it at various joints that will be obvious and also at the brake cans and slack adjusters.
15000 miles is the standard service interval with the driveshaft requiring lubrication every 5000 miles per Monaco.