What is the best way to cook a boneless ham.

My go to way to cook this sort of ham is in one of the oven roasting bags, along with 2-3 cups of apple juice or apple cider added in before sealing up the bag. If you can, put the ham into the bag cut side down in the pan you'll be using, and close it up over the other end standing upwards. Bake at 325F for 20 minutes per pound. If you prefer, you can use cola, orange juice or other similar sort of liquid. Remove your ham when it hits 130F on the thermometer. Let it sit for five minutes before you open and remove it from the juices, the carryover heat will finish the heating job to 140F. Then slice off what you want for serving. Try not to slice the entire ham unless you plan to eat it all, because the juices leak out after cutting and you end up with dry slices. Slice what you want to eat, slicing more if you need to- and keep the rest in one piece. And although it isn't the most photogenic way to do it, your ham will stay moister if you keep it cut side down on the serving platter too.

Try cooking in a slow cooker (hopefully you have one that is large enough to fit the ham). I did this once a few year ago. My ham was large so I covered the cooker in foil and put it on low for 4-5 hours (my slow cooker tends to run hot even on LOW setting). Check at the 3 hour mark. No extra liquid necessary since there would be a lot of liquid exuded from the ham itself.