I want a sales by customer detail report including GST amount. Here all sales reports shows without GST amount. Which sales report give sales including GST amount ?

You can customise the sales report showing the tax details, nuvanto-bio.

I'll show you how to add the Tax Name and Tax Amount on the Sales by Customer Detail report:

1. Go to the Reports menu.
2. From the search bar, enter the report's name.
3. At the upper-right, click Customise.
4. Go to the Rows/Columns section and click Change columns.
5. Check the Tax Amount and Tax Name box.
6. Click Run report to refresh.

For more detail in handling reports, you can check out the Customise reports in QuickBooks Online page. 

Let me know if you have other questions. I'm just here to help. Take care!