Good luck on finding a diagram but I will tell you is u start at the transfercase and work you way to the rear of the truck there are some grease fittings in that area don't know if that is all of them but that's the ones I have found cause everything in the front end are sealed bearings
I'm not sure of a diagram that you can get online, just go look at a Chilton's at your library for about 2 minutes and you will get the idea. There aren't all that many of them IMHO so you can get the idea pretty quickly. Most of them are just these quick lube points that feed more than one. It's like like something from 1970 where each component has it's own lube point.
I'm glad sometimes that I'm not as "in depth" with DIY on car fixes to know where the lube points are on a 4x4, but I can see where it would come in handy to know this.
My 1987 has a whole slew of zerk fittings on the transfer case, drive shaft, a-arms, etc. It is almost impossible to find them all, and I spend at least 1/2 an hour greasing them all every few months or so. A diagram would be nice to have. An 08 ought to be much more simple as far as finding the serviceable joints. I haven't worked on one though. How many lube points are there?
I don't usually do the lubrication of my truck. Since it is done no that often.. When it is in the shop for a check-up.. that's the time I consult mechanics if it should be done.. and let them do it.