What's a good white wine to go with an asparagus risotto? Would a Riesling work well??

Riesling is a good choice. I also agree on sauvignon blanc. While I like prosecco I don't think of it as a dinner wine as it's sparkling, crisp and low alcohol (10%). However if the asparagus risotto is an appetizer or first course it might pair up in that context.

Gruner Veltliner somehow seems to have been made for asparagus and artichokes. So glad we have it available in US these days! ;)

Prosecco would be nice or maybe a saviagnon blanc, IMHO.

Rieslings are popular with asparagus in Germany, where asparagus rules the table in spring. You might find a good Gewürztraminer from Alsace, a Silvaner from Franken (northern Bavaria) or a Grüner Veltiner from Austria that would also pair well. The trick is finding the right wine that wil work with the asparagus, so check with your wine merchant for his/her recommendations.