Is it possible to get email notification on who has not started a survey after certain days?

Hi Phoebe2022,
If it's practical, I'd first suggest just downloading the distribution history directly within Qualtrics after 7 days. It contains a column which shows who has started the survey, finished it, etc. Anything beyond that is going to be more complicated.
If you have access to API (and you don't mind a bit of coding/trial and error), you can use this endpoint to list the history of a particular distribution (this works similar to downloading the history within the Distributions screen in Qualtrics). Note that you might need to use this endpoint to figure out the ID of the distribution you want.
You could set up a workflow to run after a week (or daily, if you need) containing a Web Service task that fetches the distribution history. Then you could use a Javascript task to gather all of the respondents that have not started the survey, put them in a list and send them with an Email task.
Good luck!

bgooldfed Thanks a lot for your reply. I will give it a go - no experience with API or Web Service task (yet) though.