How in the world do I open TH3 in Sonar Artist?

Drag +Drop TH3 from Plugin-Browser to an Audio Track. In the FX-Section of that Track TH3 appears. Doubleclick on it and the window for TH3 will open
 
But I#m not sure, if TH3 comes with Artist. I have Artist and SPLAT (and CbBL), maybe Artist uses the Plugins that come with SPLAT . . .

TH3 comes with CbB so it must come with Artist as well. 
It is listed as an effect so you have to insert it into an Audio tracks Effect bin. 
Right click the Track effects bin and choose the insert audio effect option. 
Or as said above drag and drop it from the browser.