Regular 'Super Glue' works really well, its clear and strong. In my experience its more about the application than anything else. Most glues are shiny when they dry, so when you're piecing the skull back together opt for application of the glue to the backside of the two pieces vs. the front so it doesn't show. I have a fair amount of the bear skulls that are brought in each year for euros that the hunter(s) decided to do a 'zombie double tap' with one to the head

. Its a Tetris game putting the skull back together...I usually put a very small amount right along the edge of the two pieces that are going to be put together and then re-gluing on the backside once the first amount dries. If you get a lot on the outside that is showing, a
very small amount of acetone on and CLEAN paper towel will remove the excess before it cures fully.
Best of luck!!
Joel- BlackRiver Taxidermy