1. To which level does the class diagram detail to
It depends on what level you choose. I chose a conceptual high level where no attributes or methods are displayed.
2. Should we show all the associations between classes.
Yes. Which ever is applicable logically to make the reviewer understand the diagram
3. To use or avoid the "uses" relationship ?
I dont know why one would want to avoid any kind of relationship. As long as it makes sense to you, you can relate classes the way you want to.
4. Necessity of showing linkages between domain objects and controller/EJB Bean classes.
Even at a high level a basic relation is necessary.
5. Other points to take care of ?
Document your assumptions and check, check and recheck your solution. Have someone review your solution in the end so they can tell you about any points you missed out.
Also - Do we have a link to a standard class diagram which can get a score of 40+ on part 2 :-) ... Maybe a standard pet store class digram somewhere ??
Trust me you dont want to do that. In the real world we have no standard diagrams. Its all about confidence. If you are confident about your class diagram and you know it will work out, things will turn out great.