When a course is created, it gets an unique identifier known as the Course ID. The Course ID is useful when (un)assigning courses through a template.
Through the URL
The Course or Learning Path ID can be easily found when you open the requested training. Look at the URL and copy the number after cid= at the end.
Use the Report Builder
In the Report Builder, create a Courses Count Per Course Report or Learning Paths Count per Learning Path Report. On the left, add the Course ID or Learning Path ID as a field. Run the report to find the ID that goes with the training.