Hello Marc,
We're here to help. Are you using the pre-installed OneNote app that comes with Windows 10? Or the one with licensed version of Microsoft Office (2013/2016/365)?
To know more about enabling handwriting recognition, you can check NeilPR's post here.
For more information on using OneNote on Surface, click here. For OneNote FAQs, you can check it here.
Let us know how it goes.