Your OpenBuildings Energy Simulator projects are saved within a Workset folder. The below shows how to quickly find and access this folder.
If you are unsure where your Workset folder is, please click on File:
Then, the location of the project will be shown as below. Right-clicking on this will allow you to 'Open Folder in Project Explorer':
For more guidance on the folder structure of Workspaces and Worksets please see this article.