What can I use to repair a missing wing tip on my cement angel?

This should do the job for you. I know it's the glue my husband used to build a concrete stone wall. https://www.youtube.com/watch?v=O47aMCS2cpw

Do you still have the tip of the wing? If so, the above suggestion is great. If the tip is lost, go to a craft store and purchase a silicon mold kit and some waterproof plaster powder. Follow instructions on mixing the silicon and cover the remaining wing tip with plastic wrap(very tightly and as smoothly as possible. Apply the silicon mold mixture and let dry. Slit down each side and slowly peel the cured silicon mold off. You now have your mold. Tape your silicon mold together except for the top edge which will be the opening for you to pour your plaster in. Mix your plaster and pour into the mold. There will be seepage but you can clean up your edges after the plaster sets . Carefully remove the silicon mold and clean up the new wing tip. Attach with Liquid Miracle.

how crafty are you? polymer clay is good to make the wing tip and it will dry as hard as the cement. you can then paint it... but you need to know how to model it.

Modeling clay.

Thanks Peggy, but it is a cement statue and will be outside.