Email trigger and unique ID number

You should be able to pipe that into your email subject or body - Response ID is unique to each response, but you can pipe in any of the data fields.

how is this brought to the email body? is this a setting?

Here is the support article for piped text: https://www.qualtrics.com/support/survey-platform/survey-module/editing-questions/piped-text/piped-text-overview/
Most of the examples and screenshots are for piping in within the survey design. But it's the same idea. You click on the button for piped text and choose which field to bring in.
They don't give you the ability to do that in the subject for some reason. So just do it within the body and then copy into the subject.