Take a look at this >>> How to Query SharePoint List Item that were modified in Last X Days with Nintex Workflow?

Do the linked solutions provide an answer you are looking for?

• Using a calculated date in a workflow and finding all items greater or less than a date
• Using a SharePoint calculated field as a value to compare against
• Using a workflow variable with a default value

If you are required to have a date AND time stamp in your sharepoint field, then you will have to use a comparison of dates instead of equals to find those for a specified day. If you want to find all of today's, then you can use a comparison to find all items in the list where a Workflow Variable who's default value is Today and the time is set to 12 AM as shown in the first example

Then you will compare the list in a query list action

Where

List Item Date is greater than Date (workflow variable)

This should only return the items who's date is after midnight today. note this will pick up any dates that are in the future if they exist.