Finding information for Python scripting in MotionBuilder can be an uphill battle. Here is a list of some of the resources that I have been able to find (thanks google). A lot of the listed links have valuable scripts in which one can hack through and decipher what each line of code does, this can be a grueling task but also very rewarding.
These are not the only resources out there but they do seem like the ones I am currently relying on the most.
Feel free to add a link in the comment section if you have any other MotionBuilder Python scripting resources to share. Thanks.