I am working as an SDET, these are my day to day responsibilities,
1) Review the nightly tests and debug the failures if any and raise issues if needed
2) If any of the previous bugs/tickets got resolved have to retest them and close the ticket
3) Open up the sprint dashboard and look the tickets that are assigned to me, move them to in-progress and start writing automation scripts for those. Once done raise PR, get it approved, Merge the branch and execute the latest tests or if its in pipeline(CI) make sure that the build is not broken due to ur changes
4) If you are added as a reviewer for any PR, review them and do the needful
5) Attend standup to give your updates/raise concerns if you are having any
6) Mostly you wont be responsible only for automating your tests, additionally you will be having infrastructure related tasks(pipeline, grid, on demand environments etc), POC's(new framework, new tools etc), so spend some time on these wisely.
7) Additionally will be getting responsibility to write Acceptance Criteria for the product which we are working on along with UT's