Are you interested in Python? If so, check out the tutorials on how to get started with Python and OpenCV on JeVois here:
then, you would basically write your detector in python, or port it from some existing python sample. For example this one:
or other hits returned by "haar cascade python" search words.
Your task then is to take the code given in such a tutorial and port it to JeVois. The Dice Counting turorial of JeVois shows how to do this step by step, though for a different vision algo:
One last thing is to access your xml files; if you put them in JEVOIS:/share/eye.xml on the microSD, then you access them as /jevois/share/eye.xml in your code. Basically, the root of the microSD as exported by the "usbsd" JeVois command is accessible as /jevois/ from code.