Hi,
The DA-20 Katana actually does not have a nose wheel steering. The nose wheel is a free castor type, similar to a grocery shopping cart. You steer the Katana by differential braking. So rudder pedals with brakes would be needed. If you don’t have a set of pedals, I believe that you can assign a steering function in PlaneMaker.
To do this open PlaneMaker.exe. It is located in your main X-Plane11 folder. Once PlaneMaker has loaded, go to File, then click on Open. A list of all your installed aircraft will appear. Select your DA-20 Katana, and click on DA-20.acf. ( I do not have the Katana, so I don't know what the .acf file is exactly called. Could be Katana or something like that) Then click on Open Aircraft at the bottom of the page and wait for PlaneMaker to load that .acf file.
Once it is loaded, a large picture of the Katana should appear. Click on Standard, and then select Landing Gear. Under the Gear Loc tab, go to the bottom, and check if a green tick mark is set in any of the little boxes for castors. Remove that tick mark and your steering should be activated.
It then should look like this:
http://puu.sh/EDYDf/40eb117ee2.png
Save the file before quitting PlaneMaker and then reload your Katana.
Hope this helps.
Werner