Gluing sanstone

If the chip is large enough to drill and put a dowel in this would be the best option. If its to small make sure all lose is cleaned of before sticking. A resin would be the preferred method

Yes you can by using JOLLY (r) is a mastic made on combined synthetic resins basis. It is mainly used for gluing and filling all types of marbles and natural stones. Thanks

Yes depending on size they can be glued back in place. Depending on size and position of brake i:e on overhanging edge or corner I would advice on drilling and pinning if brake is large enough. If small just scratch up both surfaces (deep as possible without causing more damage) and bond with epoxy or polyester resin can be coloured to matched to stone or keep away from surface to stop staining and point with mortar to match colour of stone.

I would recommend replacing the coping if possible. Sandstone is very porous, making it fairly hard to get a clean joint without staining around the affected area, unless rubbed back this is pretty much guaranteed. 1 Doweling has the potential to create more problems, such as swelling dowels this will cause further cracking. Replacing the coping would insure longevity.