Hello,

If you are using project as part of your customer and supplier account posting, you can run relevant Open Items report.

If you want on-screen query, best place, as per my understanding, are Customer Ledger and Supplier Leger Repost windows.

But in general, closing project you should start from Balance analysis window, to see all assets and Liability accounts with balances using your project id.

From my point of view, it is not AP and AR items impacting project closing process most, but not completed PO lines, Project transactions, Preliminary customer invoices etc.
In my current workplace, we are using quick report listing all kind of transactions blocking completion of the project in IFS/Project, once project is completed in Project module, accounting team is using balance analysis to reclass balance items accordingly and only after this reclass entries we can close project.