Hi @Shashi_Mulugu,
I am afraid that this functionality is not supported by Touch UI yet. If you will look into Adobe documentation that describes status of migration of specific features from Classic UI to Touch UI, you can observe that this specific one is marked as Missing, and Classic UI is recommended for now.

Here is a link to the documentation: https://experienceleague.adobe.com/docs/experience-manager-65/content/release-notes/touch-ui-feature...
It is for AEM 6.5, but I think it is the same for AEM as a Cloud Service.
In my opinion you could also raise an Adobe Support ticket to get more information in terms of when it can be expected to have Subscribing to Notifications available in Touch UI.