... we are unable to get the option as per screen shot below.

I tried to reproduce the problem by using the ClientUI live sample with no luck. The "SubReport" option inside the Ribbon can be found. See screenshot below:

The step-by-step below shows how to show the "SubReport" option in Report Designer.

1. Open "Sales Comparison" reporting sample (live).
2. After the report appear, click "Design" button from the toolbar to open the Intersoft Report Designer.
3. Click the Ribbon Gallery to show the "SubReport" option. (it is shown in the bottom-right of Ribbon Gallery, see screenshot above).

Sub report allows you to embed one or more reports into a single report document. This can be useful when there is a particular report structure which have a consistent appearance and functionality that needs to be included many times in a report.

In the "Sales Comparison" sample, the sub report shown side-by-side. ClientUI documentation provides walkthrough article, Create Side-by-Side Report Using ClientUI Reporting. It provides step-by-step instructions to create a side-by-side report using ClientUI Reporting including designing the report by inserting two sub report into the data band. Each sub report will display different sales based on the selected territory.

Hope this helps.