I’ve repaired skulls many different ways. Super glue the pieces together and quickly add baking soda to the glued seam. It dries really hard. Some I have done this then used bondo with a cream colored hardener. Sanded it all down smooth then painted with an air brush using off white. I’ve also used apoxie sculpt but I prefer the glue, baking soda and bondo method. Also, super glue has a tendency to turn yellow. If I just wanted to use glue then plain old white Elmer’s glue is the best since it won’t turn yellow.