We are moving data from sharepoint to Google Drive and many files are checked out and can't be moved over. We need to find all the checked out files. How do we do this?
This question is quite common and one of the universal solutions is to run some PowerShell locally and retrieve a list of all such files. The problem you are facing is SharePoint hierarchical structure (Site Collection > Subsites > Document Libraries > Folders) and you would have to crawl up to the last level in order to make sure you got all the files.
You can find such a script here, but as Mike points out in his comment in all depends what exactly you are moving out of SharePoint. In any case, it is a good start but will require some work.
Commercial tools like SPDocKit can also retrieve such reports. (Disclaimer: I am affiliated with this company)