Can any one tell me how to get the "strum" keys to work when the synth is in Guitar Mode? I was expecting that a combination of a keystroke for the chords and a keystroke for the strum pattern would result in a strummed chord, but no joy there...  The strum keys played alone just produce a "thunk" noise irrespective of which strum pattern key is played.  On the plus side I can get major/minor/7th chords - so that bit works: its just the strumming that has me flummoxed.

Plenty of videos for you to watch and discover how it works.  YouTube is the visual instructor these days. 
 
https://www.youtube.com/results?search_query=Strum+Session+2+
 
 

Thanks for this response.  The problem I have is that I am doing what the video tells me - but I am not getting the result the video says I should.  (maybe I should have said that in the first place) I have tried the obvious stuff and got nowhere. That is why I am asking the question to the community: to find out how others have got it to work in Sonar....  It works fine in loop mode, but not guitar mode - can you tell me how you got it to work for you?

The "thunks" you are hearing are the strums. Now you need to give the strums a chord to play. Go to around 2:40 of this video to see how to solve your "problem"! 
 

Thanks for your response, yes I can do that: it works, but its not the quick and easy use promised.   What I can't seem to do is this:
https://www.youtube.com/watch?v=klGmlqVQ-vc  at 1:20.   When I do what he is doing at 1:50 i get either single notes or "thunks".  Does this work for you or is this a feature that has been taken out of the sonar editions?

   I think there is a CAL called STRUM. I've never used it so I don't know how well it works but it might be worth a shot.

Using a keyboard, are you holding down the chord keys, while playing shorter notes with the strum keys? E.g. hold down middle C while using the octave C above to play down strokes?
 
In the piano roll you might have to sort out the base octave to ensure Strum receives the correct notes.
 

richardskeltmusic
Thanks for your response, yes I can do that: it works, but its not the quick and easy use promised.   What I can't seem to do is this:
https://www.youtube.com/watch?v=klGmlqVQ-vc  at 1:20.   When I do what he is doing at 1:50 i get either single notes or "thunks".  Does this work for you or is this a feature that has been taken out of the sonar editions?

Open the manual (click on the chevron above the Strum logo (pick) and then click on Strum Session Manual or Strum GS-2 Manual, as appropriate) and read section 3.2, starting on page 14 (Session) or 20 (GS-2), at the bottom.
 
Only the 'C' (downstroke) and 'D' (upstroke) strumming keys produce strummed chords. The Arpeggio keys (1-6) play the corresponding single key in the arpeggio, and the Palm Mute and Mute keys do what they say. Check out the Automatic chords.
 
The manual covers this all pretty well.