how can i use arcgis javascript api and dojo toolkit in Visual Studio .Net Projects?
Could you be more specific with you question. Esri JS API and dojo are both javascript frameworks. You use them in a web applicaiton it doesnt matter if it is java or .Net. its alway the same add the link to the scripts.
If you are asking how to start using it then you should start with this tutorial
Build your first application | Guide | ArcGIS API for JavaScript