How can I know the type of an airplane before reservation? I want to know if it is Boeing or Airbus and the model if it's possible. Can I use websites such as SkyScanner for this purpose?
You can absolutely find out this information before booking, though it is subject to change. Kayak definitely provides this functionality when opening the details of a given flight. See the image I've included below.
In addition, most airline sites also provide this information. However as far as I can tell, SkyScanner does not provide this information - or at least not where it's easily findable. I've attached the corresponding SkyScanner information for the same flight, noting that there's no plane information provided.
You can enter your flight number/information and see your plane from the booking panel, SeatGuru, FlightAware, and many more sources.