In DotSpatial, the Shape class has a ToGeometry method.
/// <summary>
/// Converts this shape into a Geometry using the default factory.
/// </summary>
/// <returns>The geometry version of this shape.</returns>
public IGeometry ToGeometry()
{
return ToGeometry(Geometry.DefaultFactory);
}
Edit
I've only used the dotspatial stuff for projections, so I can't really help you too much.
1-2: Not sure. The code is open source if you want to look and see what they do
3: WKT is a human readable text representation of the geometry. I would assume that it's the same value as the file, but I don't know. Again.. check out the dotspatial source code
4: The prj file tells you what projection the geometry is in. Depending on what you want to do with it, you might have to re-project it. Things like Bing Maps and Google Earth use a mercator projection, for instance. The dotspatial projections library is good and makes it easy to transform the geometry from one projection to another.
I've done quite a bit of work with shapefiles.. let me know if you have more questions.