To get started with MediaLab, you may want to run through the samples within the samples directory.
It may also be beneficial to read through the help files.

It sounds like DirectRT could fit this type of experiment better; however MediaLab will work.

One way of accomplishing your task would require using the duration (d) parameter to take the user through each questionnaire and then denote a 'SkipTo' option if they answered the question correctly.