How Do I Get Wallpaper Glue Off Of Wall?

Rent a steamer for removing wall paper or find some other way to use steam. You may be able to get away with holding a hot,damp rag against the wall and remove it that way but go slow so you don't tear the paper on the drywall.

After reading your question, it sounds like you have already removed the wallpaper and wallpaper backing.
  If this is the case and you have glue stuck on the wall, (it depends on what type of glue the wallpaperer used), but you can try using a cleaning product with orange/citrus in it . Let it sit for 2 or 3 minutes, then use a razor scraper at a 45 degree angle to scrape the glue off.
  If the walls underneath the paper are painted with a semi-gloss/ gloss paint, then you can use GooGone to remove the glue, but you will have to scrub it down with some dishwashing liquid afterwards because the GooGone has a citrus and oil mixture. It is a great product to remove sticky stuff and comes in a spray bottle. You can pick it up at most any supermarket in the cleaning supply section.
  Septic is right with his answer on how to get the wallpaper off the wall.  A steamer works great, but if you don't have access to one, then you will have to remove the wallpaper the old fashioned way, which is to pull the top layer off, then use a sprayer with hotwater in it to spray the wallpaper backing. Let it sit a couple of minutes, then use a putty knife to scrape it loose and then pull it off.

Get a sponge