ZedGraph: просто точки

I think your solution is on The Code Project. Have a look at the part where he talks about "The Fill class". There is a dot-only example.

The Scatter Plot Demo from ZedGraph's site shows how to do it. There is an IsVisible property on the Line which you set to false to only show the points.

LineItem myCurve = myPane.AddCurve("Title", list, Color.Black, SymbolType.Diamond);
myCurve.Line.IsVisible = false;