There are several ways to find the project ID of project in TDM Portal or Datamaker.
Click the gear icon next to the project/version dropdown, click the project for which you want to look up the project ID.
On the details screen expand the Project Settings.
Select the project/version for which you want to look up the project ID.
Right click in the Context line, a pop-up is displayed with all the ID's of the selected context.