Use root explorer to navigate to /system/media/audio/UI/
in that folder three of the files are the Spen Ogg files (Pen_att_noti1 2 and 3).
Whatever sounds you want to replace the stock sounds must be renamed and placed here.
Rename one of the old files (pen_att_noti2.bak for example) then rename the new Ogg file to the original name of the one you renamed.
Sent from my SAMSUNG-SGH-I317 using Android Central Forums
These are the directions I followed - you have to be rooted
[MOD] LightSaber S-Pen sounds - xda-developers
here is a bunch of sounds
[Mod] Custom S-Pen Att/Det Sounds - xda-developers
enjoy