An easy way to get "there" with any automation is to simply click the "W" - for "Write" in the mix window (console view) - and then manipulate the channel strip - volume - pan - etc.  This is helpful in my experience  as sonar automatically creates an envelope for the parameter you want to manipulate.  Say - you want to add a high shelf to an eq on your guitar buss - but only for the chorus.... click the W - open the lug in and just click and drag the eq in real time and sonar creates the specific envelope for you.  There are times in a mix when I will want to do a complex effect manipulation - like for example - on the last note of a rock star guitar solo - lengthen a decay time of a reverb, while also increasing the intensity, spread, and mix of it.   For something complex like this - its super easy in sonar:
 
Go to the last note - arm the "write" feature - open the reverb plug in - press play and simply click on each of the controls I want to manipulate - in this case - decay, drive, spread, and mix.  Sonar creates each of these envelopes individually, Ill then loop the section of the audio and go back in and fine tune the effect automation.  
 
MAKE SURE YOU TURN THE WRITE COMMAND OFF so you dont dig yourself a hole=-)
 
 

You can draw automation in buses, the problem is that the Aim Assist line, which is so useful for positioning nodes and edits in the track pane, does not extend down into the bus pane. It's like they've never turned it on down there (hmm that didn't come out right )
 
I posted a feature request about this ages ago which got a good number of votes but who knows if Cakewalk reads the feature request forum. Anyway you can vote for it here http://forum.cakewalk.com...in-buses-m3102234.aspx

Sharke if they didn't, there would be no point in having a Feature Request forum.
 
And yes, the absence of Aim Assist in the Bus pane can be a complete PITA

Thanks konradh, that's exactly what I want to do.  But can;t find where to insert the bus filter... in this case for my drum bus to automate the bus volume... the only think I can see that sounds similar to Output Level is "Drum Send Level"... is that the same thing ?

No.
 
Just right-click your bus fader and choose Write Enable. Play the project and move the fader.
 
When you've finished, do 2 things - 1st UNcheck Write enable, then 2 - go in and manually adjust/fine tune the individual nodes you just created