i have some five problem like this can u help?
1.Cargo Tracking Management System
2.Supermarket Sales and Inventory Control System
3.Emergency Call Management System
4.Job Management System

I want to what are the entities of these problems?

You didn't show any problems. This list is only about things that you need to analyse, study and take care of.

When you have to create an database model you need to understand what are you modeling in the first place.

We can't tell you the entities for those systems, because it depends on the level of details that you're going to implement. A Job Managment System could have 5 or 25 entities, depends on the requisites for your project.

It's no use creating a super database model if you don't have the time, knowlodge or the resources to implement it all.

If you are not familiar with entities and entities relationship I suggest you study them a little bit before enter a specific cenario.