Web API returns JSON data by default and your presentation layer could be web / winforms (not very much recommended)
- Can i in the same controller return the data and the view or do i have to create another controller?
The same controller can be used for both web & winforms(winforms is not recpmmended)
- After that how can i call the view from a WinForm app?
My understanding is that you will not call the view from the winforms. views is the presentation layer which renders HTML output for the web. You may needs to call the API's from the winforms rather than calling the view?