How to create / assign automation envelopes for Kontakt?

This has nothing to do with Simple Instrument Tracks - lingyai obviously has access to Kontakt parameters in the automation lane's edit filter menu - you don't need to split a SIT in order to access the synth's automation parameters.
 
Lingyai - I think what's going on here is that you are trying to automate a Kontakt instrument that doesn't expose any of its parameters to Sonar. Try loading up something from the Kontakt Factory Library - you'll see that named parameters are provided for these instruments, or indeed anything else by Native Instruments. With 3rd party instruments however, it's pretty much hit and miss whether it exposes the parameter names to Sonar. 
 
If this is the case, you need to assign parameters for automation within Kontakt. It's really quite easy. 
 
The panel on the left hand side should have a tab labeled "Auto" - click on it. Here you can assign which parameters you wish to expose to Sonar. You will see the empty slots arranged into rows in the panel. Click on one of them and drag across to the control you wish to assign on the instrument, then let go. You'll see the name of that control appear in the "assigned to" row in the panel, and you should now be able to see it in the automation menu in Sonar.