If I know about a specific USAID funded project underway:
How do I get access to the data produced from the project?
Also, how can I tell if data about the said project be subjected to the open sharing policy?
Unless the data about the project is made publicly available through a repository and/or any other means or format, you will have to officially request for it from any of the parties involved.
Depending on their authority, level of access and/or any other provisions (rules, regulations, etc.) they may have relating to the said project, your request may be granted.
Other means may be to go the investigate way (whether undercover or not) or the legal way (with a legal document issued by a court that presides over them so as to back your claims).
Whatever your choice, whether listed here or not, do make sure you do your homework effectively so as to truly achieve your aim.
You may equally find this post of great relevance.