Hi @nitin4  , These "job costing" features are available in QuickBooks Online Plus, Advanced, and Accountant. Make sure your QBO is one of them. 

Turn on Projects

If you haven’t already, turn on the Projects feature.

1. Select Settings ⚙, then select Account and Settings.
2. Go to the Advanced tab.
3. Find the Projects section and select Edit ✎ to expand it.
4. Select the Organize all job-related activity in one place checkbox.
5. Select Save and close your settings.

The Projects menu now appears in the main navigation bar.

Step 2: Create your first project

1. Select the Projects menu.
2. Select New Project.
3. Give your project a memorable name.
4. Select the customer you’re working for from the drop-down menu.
5. Add any notes or details about the project.
6. Select Save.

Then, you could add income and expense project. See  this article .

Comment back if needed. Enjoy your day.