I haven't found a floating S Pen type app yet. There are some with regular text, but I'd prefer one with S Pen integration.
I was looking for a way to have contact info I wrote down with my S Pen and address book open at the same time.
I came across an app called DW Contacts. After downloading it, it added a shortcut in Multi View. I set it as the default to replace my stock address book. Now I can have S Note and DW Contacts open at the same time in split screen mode, making it easy to add or edit contacts while looking at my S Notes.