What can be put on a chalk drawing to seal it without smearing it?

you need a spray fixative that you can purchase in the art supplies section. People who do pastels, charcoal and chalk drawing use it. Fine, light misting coats.

Artists sometimes use hair spray to seal the chalk or pencil drawings,it really works

artijan

I use hairspray or hair laquer on mine not had a problem with them smudging

I think you could use a clear varnish spray paint.

They also make a fixative just for this, sold in art stores, or art section of say Walmart. But I always usually used hair spray with a very fine mist.

Spray it with artists fixative until you get the result you like. It will add gloss.