Its depends on different organisations dude.For piping design u can get some questions but software wise its difficult to get the questions.Tool test for designers is different for different organisations.
I may be wrong but pdms does not do exams!, some companies use their own questions/answers when interviewing. As kubic says it depends on the discipline whether you are designing or just modelling?
If you are looking for piping design there is a good manual on the internet 'Pipe Drafting and Design' (about 50 mbytes to download)
Attached is a piping tutorial that may be helpful?
I'm not sure about structural, electrical or mechanical and for hvac I suggest you read through Ashrea and smacna manuals
Either way I suggest the best route is to take further education, be it part time or full time to learn the specific discipline of your choice to gain qualifications. Remember pdms should only be used by qualified designers/engineers