Sonar Tuning Guide
The Sonar class hopes to produce its own tuning guide in the near future but until then the main sailmakers to the class have tuning guides available:

http://www.doylesails.com/sonar-tuning.htm
http://shoresails.com/onedesign/sonarguide.htm
http://www.northsailsod.com/class/sonar/sonar_tuning.html
The Sonar Class Association has published a number of articles on tuning and racing the Sonar and these are available at:
http://www.sonar.org/

One of the top US Sonar sailors is Pete Galloway, who conducted a Sonar Seminar covering tuning, trim, crew work, starting, strategy, and tactics. Download a PDF outline of the Seminar here.
Dave Franzel - Also one of the USA's top sailors has prepared an upwind tuning guide for the UK Class Association. Details can be downloaded here.

Pete Galloway Seminar
Upwind Tuning Guide - Dave Franzel
Dave Franzel expands on his Sonar tuning guide